DeMarcus Cousins is expeled  because of his intentional fault on Carter. He knew before,

and this voluntary fault put him out of the court.

He regrets his act but unfortunately, it’s too late and the referee won’t  close their eyes on it as they’ve already whistled and ejected him.
Watch the video here :

http://www.youtube.com/watch?v=F6pERQcPnhU&feature=player_embedded