Because he's a brilliant manager. He's an asshole on purpose, which the media happily lap up and use to portray him as such, yet, funnily enough, the players he work with say he's completely different in person and would do anything for him. To me, that's a masterclass. It's not easy to regularly better and fool the media, but Mourinho does. They didn't make him out to be a monster, he purposefully did it himself. I don't know the exact reason, although it's often suggested it's to take the pressure off of the players.
Plus, he's a character, and without people like him, sport would be very, very bland. He's passionate, and whether you love him or loathe him, you can't deny this. The PC crap most players and coaches (in any sport) conform to, bores me. On top of that, if you look past the smear campaigns, he has some brilliant quotes and points, it just so happens that few respect him/care because A. his image is so poor, and B. Barcelona's is so great. Most people are more than happy to listen to what the media has to say without reading quotes in context and thinking for themselves.
And through all of this, he's still got one of the most impressive records out there.
