Revisiting Should we have tags for separate Linux distributions? one year later.
We currently have 69 questions tagged ubuntu, 37 of which don't have the tag linux. And yet I struggle to find one where Ubuntu is fundamental to the question. Pretty much all of them are asking for software to run on Linux, not software that's related to Ubuntu. Software may sometimes be more convenient to install on one Linux distribution or another, but software that runs on Linux runs on any Linux distribution (some versions of some distributions may be too old, but it's the fault of the vintage, not of the distribution), so tagging with a distribution to say “it must run on this distribution” is wrong.
P.S. windows seems to have a lot of unwarranted fragmentation too but I'll let Windows experts discuss that.