(all of your questions answered and then some)

https://github.com/torvalds/linux/blob/master/Documentation/...

So the Linux devs are really against it both from a lack of resources point of view, and from an ideological "we hate closed source" point of view.

Unfortunately, most vendors with closed source drivers don't give a shit about ideology and simply provide binaries for very specific Linux releases. That means users end up getting screwed because they are stuck on those old Linux versions and can't upgrade.

The Linux devs have this strange idea that vendors will see this situation as bad and decide that the best option is to open source their code, but that never happens. Even Google couldn't get them to do that. This is one of the main reasons that Android OS updates are not easy and universal.

Assuming you compile a static binary that doesn't even rely on libc, then yes, something compiled 20 years ago will still run.

But in the real world you have to recompile your software constantly due to breakage in dependencies (including glibc). And a binary won't work cross-distros without adding efforts despite running the same kernel (sure, that part isn't the kernel's fault).

It's often memed that the most stable interface on Linux is win32 (via wine), and that meme isn't entirely off-base.