Eh, that's just where he got famous but he's from New York...all his street cred comes from there. He's not really any part of the West coast East Coast beef of the 90s, he just hates most East coast labels like BadBoy and Murder Inc. his beef with Diddy is personal and probably preexisting like his beef with Irv Gotti.
You gott realize, he went to them with his music first but he didnt like how east coast labels were trying to play him so he got with Em, and Em introduced him to Dre.