Maybe because all the developers ran away to Macs, instead of sticking around dogfooding and fixing bugs? Free software is a collaborative social enterprise - it's not really anyone's job to make free stuff for you to use. If, as a developer, you've taken the easy path of proprietary software for years, and now after finally getting fed up of being abused by a company that doesn't have your best interests at heart you return to the world of Free Software only to complain that it's still unpolished - then I'm afraid you are rather entitled, and deserve a serenading by the world's tiniest open source violin.
And make no mistake, the kinds of "rough edges" you refer to are not hard computer science problems. They're broadly just the kinds of everyday maintenance things that inevitably crop up in a huge software project on an ongoing basis and are easily fixed by many eyes and a little graft. The more eyes, and the more graft, the more polished the system.
For what it's worth, Desktop Linux for all its faults is still light years ahead of the competition. Far from perfect, as you say, but it really is the least bad choice. As they say - the best time to rally around Free Software is 10 years ago, and the second best time is now.