Valve can go into the negative selling Decks, something that their competitors can't reasonably do because they will get money from Steam store sales made on the Deck. I for one went from buying 3-4 games a year to like a dozen because it's been so convenient.
Seems a lot like competing launchers, a lot of companies want a slice of the pie that Valve discovered but aren't willing to do the same amount of work. I've heard good things about the Ally, at least.
More like Valve created. There were PC handhelds before, but they were too expensive, had a crappy UX, and not high performance enough. Valve produced a device that addressed each of those and created a market for itself.
If you make a compelling product at a good price, the demand will come.
Oh but that requires money and effort, and creates a fair exchange for the purchaser, no can do. Hardware companies are more focused on how to force people to subscribe to their own devices.