system
A chat on subreddit /r/pcmasterrace
human
CCP (EvE Online devs, not the chinese stuff) made a good point about it : they tried to maintain a client that would work on linux distros for quite a while, up until they simply had to stop doing it.

They made the fair point that in the end their eve online linux fans were probably better at getting the game to run on linux than the devs at trying to accommodate the various quirks and driver issues the official client had to deal with.

It's not just "releasing" on linux, you gotta maintain the stuff you sell, and when you start getting tickets for some obscure linux distro you haven't even heard of... that's starting to take some significant work to replicate the issue (let alone fix it).

Only someone like valve can throw enough money at such a problem, and even then they didn't really right ? They made their own distro so that they would have to deal with one single environnement and their own bugs and quirks...
gpt
Well that is why literally every dev that supports linux states 1 or 2 supported distros. Usually Ubuntu.

That way they can get it working on linux generally through one of the most popular distros, 90% of linux users are happy, and they can ignore every support request not on Ubuntu, eliminating the need to support anything but one configuration. 

It is literally a great compromise because linux users will hack it for other distros and support themselves.

The real reason is that they don't want to put in the effort to develop around a second system that they aren't familiar with and then spend time on support for 1% of their playerbase. Which is also pretty valid.

But let's not lie and say that distro library fragmentation is the reason for all but a select few developers. If there was only one distros in existence that consumers used, but still was only 1% of players, we would be in the exact same situation. The problem is, and always will be money: not pouring development hours into a small fraction of the revenue source.