While I won't paint with a broad stroke and say his "ghetto" personality clashed with "suburban white folks", I think it came down to trust.
Marshawn has always been huge on this. If he respects you, enjoys your company, trusts your friendship, he will do anything for you. If that trust is violated, you are dead to him I think he felt trust was violated following his first two years and was publicly never the same. When local cops are busting your balls for playing loud music at the music and about having pit bulls, local media is writing scathing articles about you and the fans are telling you to "hit the bricks", it's not surprising why he has changed.