The game has been released 4 years ago. An average worker in the US works 1770 hours a year.

10 developers working full time over 4 years (and this doesn't even include the time they spent building the initial release) would work a total of ~70 000 hours, not "hundreds or thousands" of hours.

In fact, even thousands of hours would be only a single man year.

They've released 23 content updates so far, bugfix patches are probably much more. Even just building, superficially testing and deploying a release easily takes 4-5h. And this game is not just a plain and simple flat screen game, but one that supports SteamVR, something that's not remotely trivial on Linux.

Even a single non-trivial bug can cost 20h of total work time from support handling the report, a dev reproducing it, the bug going trough refinement, bugfixing, code review, testing, deployment and so on.

I guess you haven't worked in a real company before and don't know how project management and processes work. Stuff takes a lot of time.

And believing that Unity just magically abstracts all OS-specific bugs away is very naive.

And it's ridiculous to claim that they are dropping Linux support after 4(!) years because they are too incompetent to figure out how to support Linux. Obviously they could support Linux just fine from a technological standpoint.