I can understand extreme cases, like some sort of disputed IP where their contact to sell the content turns out not to be with the actual rights holder, resulting in no longer serving the content (with an unconditional full refund). But past that they should be legally required to host the content until the heat death of the universe.
They could have not given you root access and forced you to install your own OS for it to manage things that aren't on Steam. They could have locked the bootloader and refused to install anything they didn't sign.
Neither would violate the license provided they made the source available.
It means the core OS is isolated from all the functionality in a way that allows you to modularly add all the functionality on top of it in a reproducible, robust way.
In theory. I haven't actually dug into any of them personally.
It's a 2D platformer. Technology is no longer the limitation.
That's the reason the value proposition is so bad, too. It's not that there's anything inherently wrong with any of the 2D Mario (or the rest of their 2d side scroller catalogue). It's that they're charging full AAA game price for content any indie can match at everything but the specific IP (and many do better).
Some of their ideology helps their games last the test of time reasonably well, and they're the biggest publisher that's so heavy in 2D side scrolling stuff, but the reality is that it's now so easy for a solo dev to publish in an extremely polished format that there's very little they could do that would justify their price point.