Because Billy Corgan in a compositional genius. Both from a music and lyrical perspective. Of course he's a great musician from technical perspective, but that's just icing on the cake.
Whether it was the early Pumpkins, later stuff, Zwan, or his solo career (c'mon, seriously. I can't think of more than like 2 electronica, artists that have ever done a better job than Corgan did), Mr. Corgan has done an excellent job as an ARTIST, exploring and expressing the nature of the human soul and the spirit of Chicago with melodies and lyrics like no one else.
Everything I have ever done on an artistic level has been compared to the works of Mr. Corgan.
(As a result, I have very low self-esteem. Thanks a lot, Billy... hah, jk.)