Its really because of Adult Swim Nostalgia like alot of others have said, but his beats are genuinely some of the best hip hop instrumentation of all time, like the Prince to JDillas Michael. What they were able to do within their soundscape is generally seen as special no matter how off base his rhymestyle is in comparison.

An acquired taste but an important one as far as Hip Hop goes. entire underground platforms like Soundcloud owe their existence to this man as far as what he was able to do for alternative Hip Hop. Remember All Caps when you spell the man name.