YouTube is running an experiment asking some users to disable their ad blockers or pay for a premium subscription, or they will not be allowed to watch videos.
Although not nice for people that can't afford or don't want YouTube premium, this makes a lot of sense. Hosting videos costs a lot of money, and I doubt the YouTube Premium subscribers pay even nearly enough to pay for the hosting of all these videos. Personally I just have YouTube Premium as this also gives more money to the creators that make these videos.
I think an Open Source alternative would also have a lot of trouble with receiving enough funding to stay up. It would require a lot more donation compared to hosting mostly text based sites like Lemmy.
I think GP is saying the the total income from Premium doesn't cover the cost of running all of Youtube, not that a single premium subscription doesn't cover that one user's costs, which it obviously does (or the people running YouTube are truly idiots).
Peertube I think helps offload that by having every video be a torrent so each additional viewer increases the max bandwidth. But still not free to start