imo, it was a combination of chasing generic hit records and being an insufferable a$$hole....the beefing with everybody and bragging about sales got real annoying...so then, people started rooting against him because thats how shyt go, especially if you winning and popping shyt about it all the time
think about the fanbases he alienated.... going at Wayne while Wayne was on the cusp of taking over was a huge miscalculation
the irony is...while he was flopping commercially, he was making

shyt for the mixtapes...i always wished he wouldve said fukk the sales/top 40 shyt...and just focused on making a cohesive album full of that aggressive content he was always talking about...do a concept album or some shyt and just talk that shyt...but he got stuck in time when it came to making what he thought would be hit records because he wasn't comfortable with the inevitable fall off...nobody sells 8 mill every time out but he acted like he was going to and left himself vulnerable to people partying on anything less than that even though its standard to tail off in sales after the 3rd joint