> All software maintainers have to do is not touch it

That seems okay...

> and not break it

Ah, there's the rub - when you're not actively testing on the platform, because no-one on your team has the relevant pieces around any more, then you don't know whether you've broken it.

And even if you do have the relevant pieces, there's a non-zero cost involved in testing every subsequent release on that environment, and implementing workarounds for every subsequent change or new feature in the future which fails to work on the old hardware, used by ~0.0% of your user base.

It's not just boredom that causes stuff to be dropped, it's when the cost of maintaining compatibility with the old hardware exceeds the benefit of retaining the compatibility.