He's been an ally for a long time and he does make great music. Plus his artistry and image as a rapper, moving away from gansta rap in the 2000s, his ventures into fashion, and all that probably make him more relatable than other rappers?
His music is stellar, he's talented, he's extremely outspoken, he creates controversy, he divides opinion -- the media often uses him as a scapegoat, etc.
Personally, I feel like he and Lady Gaga are quite similar.