Thousands of Portuguese protest for the right to affordable housing

I don't disagree with the sentiment of your comment, but I feel it lacks some nuance.
First of all, where are those empty houses located? A lot of the pressure is in larger urban areas: Lisboa, Porto, Braga, Coimbra. If the houses are away from an urban centre, they might as well not exist.
Portugal also has a huge emigrant community, and it's common for emigrants to have a house back in the home country, usually in more rural areas, but not always. These houses are a little retirement plan, and tend to stay unoccupied for months or years, only used when that owner goes to Portugal on holidays, or when/if they decide to return.

It's not that linear here.

There aren't huge corporations amassing houses and apartments here and asking insane rents.

This craziness started back in 2010, after the 2008 market crash. Interest rates were fairly low before the crisis and that allowed for many people to buy their family home. When the market crashed and interest spiked, many lost those houses but somehow most people endured the crash.

Next comes an historically low point for interest rates. Many people with some income buy second homes to rent and invest into air bnb. The market remains stable.

CoViD hits. And tourism, the biggest industry in the country crashes and does it hard. After the lockdown, our equivalent of air bnb was quicker to pick up due to individual tourist looking for that alternative.

When everything returns to normal, we get a flood of tourist and a new phenomena: foreigners looking to settle in our country to work remotely.

We are very affordable for the so called "digital nomads" so this drives up the rental market. Real estate agencies move up to control the rental market, promising ever rising leasing prices, which happens, has the market moves to fetch higher prices from foreigners that can afford it and to scare off other foreigners, often immigrants, with less money to rent.

Between a speculation wave and a populist wave, the nationals get crushed in a leasing market where private landlords feel they can extract a lot of money from sub par houses, often aged and with no appliances. Buying has become more difficult, due to higher interest rates and ever mounting prices, which foretells a bubble forming.

Oh, and an added nail to the coffin: the state has published tables with so called "affordable leasing prices", for guidance of the landlords, but even those are ridiculous, with an apartment for the average 4 people family costing more or as much as one month of salary. The prices change from area to area but are nonetheless ludicrous.

Finally we're on the news for something meaningful, and not for being the best destination for whatever.

There is a great deal of backlash to the Golden Visa programs which were set up in Europe to boost foreign investment and skim more foreign money into government coffers. While it did result in some building and some influx, the impact has been wildly overstated.

Before I’m beset with angry residents, I’ll note that last year, there were 168,000 real estate transactions in Portugal, but there have been less than 10,200 golden visas granted via real estate purchase over nearly twelve years. That’s less than 850 real estate transactions year, on average, or around 0.5% compared to the 168,000 last year.

There are, I’m sure, edge cases where a large residential building was bought, renovated, and then resold mostly to foreign investors- I’ve seen the ads. But as a driver of housing rents I’m skeptical that such a low volume has been the primary driver of rent inflation. I’m seeing ridiculous rents everywhere, and I think it’s a combination of Airbnb-style landlords snatching up inventory for short term rental income (which no private renter can afford nor private buyer/homeowner compete) as well as the condo-bros leveraging their way into tens of hundreds of units for the passive income fad that has swept most of the western world.

It is probably a combination of wealthy foreign migrants and overtourism.

Portugal had been pushing visas for remote workers around Covid similar to how a lot of poorer cities and states have been pushing for remote workers to move in. Apparently it has been very successful, causing people to get pushed of Lisbon's city center.

Portugal has also been selling itself as a way to get a cheap European vacation in the USA, which has also helped. I know United Airlines opened up a lot of flights from Newark to various Portuguese cities. Porto has become swamped with AirBnB's as the city shifts to a tourism economy.

Given that Portugal has economic statistics similar to Eastern Europe, I can see this pushing out Portuguese from their cities and into Newark.

New constructions for habitation in Portugal over the years.

This, plus the fact that the last 30 years have seen an increase of 0 in real term for wages, plus a government that has done nothing over the best economic years we had from 2014 to 2019, and massive unchecked immigration(that has already received negative notes from the EU as illegal), and you have the ingredients for a nice habitation disaster, which is what this is.

Oh, and no effort to create good public transportation to connect cities to make reasonable living outside Lisbon. Or even try to push job creation out of the Lisbon district. And this is all before we talk about all the governmental decisions that have done nothing but decimate the renting market.

Speculation has its hand, but it pales in comparison to good old fashioned mismanagement of the state.

The country has a Communist Party who are pro-Russia, put Party above everything else all the time, haven't updated their slogans in over half a century and until not that long ago were Stalinists. They are quite literally dying as a political force as their supporters die of old age (and given Portugal's relativelly high life expectation, you can imagine just how ancient most are).

Meanwhile the newest ecological party just went into a coalition with the mainstream Right and the convervative traditionalist Right (who are the leftovers from the Fascist days) in regional elections. I would love to hear how exactly Ecology is compatible with the kind of core policies of the mainstream and conservative Right, like the Consumer Society.

Meanwhile the supposedly Thinking Leftwing party is busy parroting the Liberals (i.e. neoliberals) of the US and UK (which are countries far more to the Right than mainland Europe and were those movements "strangelly" never worry with wealth inequality) and have no actual vision for a better Portugal, spending their time running in firefighting tactical mode running after the news (they're led by people in their 30s with zero professional experience outside politcs). Also they're painfully established middle class (the scions of well-off families) and most definitelly interiorized the whole idea that trying to get what's better for you and those like you is fine, aka Greed Is Good.

Unsurprising the only growth you see in Portugal is an ultra neoliberal party which looks suspiciously like they've been launched with money from what Steve Bannon brought to Europe a few years ago for that (their launch marketing material stood out as done by the kind of real expensive international marketing company that a party that size can't afford and they rely mostly of ex-finance types to front them) and a nationalist fascist-inclined populist party started by a guy who was in the mainstream Right party were he didn't get any really big money-making sinecures, became a TV soccer commentator and then leveraged it to make a (surprisingly successful) far-right populist party.