Their Mac codebase likely isn’t that Unixy.

Also, Acrobat Reader has been available for Linux (https://linuxconfig.org/how-to-install-adobe-acrobat-reader-...).

I guess they abandoned that because of the support load required (supporting Linux can be hard because of the proliferation of distributions with different directory layouts, font engines, etc. Most users may be on one of at most a handful distributions, but the few that aren’t can cause high support costs)