This should be pretty obvious, while I don't think either would ever publically admit the extent of just how deep this beef really goes. You don't have to be a genius to figure things out, people don't just leave labels and labels don't just let profitable artist walk. Just check a few of CuDi's comments on Indacud...
Kid CuDi - Cold Blooded
"the lost black sheep of G.O.O.D. Music/ Only good for a hook, huh? Let me show you flows"
Kid CuDi - Burn Baby Burn
"still don't feel appreciated and not by my own fam/ all good I'll be tucked away in them shadows"
Kid Cudi - Lord of the Sad and Lonely
"My label fukking up my flow, see I'm getting pissed/ work too damn hard dog for their shenanigans'
IMO I think CuDi didn't like how the label was handling his music and his lack of presence on Cruel Summer was the final straw.