There could be several reasons why Mara left. I don't think it was the money.
My feeling is he left because of Cronin for two reasons;
1. He didn't care for Cronin's tirades.
2. He didn't like the way he was being used. Specifically on defense. Cronin was having him running from the low post to the top of the key incessantly, expending energy that Mara is yet to handle. Maybe Mara sees himself strictly as traditional low post player. Also, he might see himself as a starter and felt his future at UCLA was coming off the bench.
Of course, I may not know what I'm talking about, but it does seem so strange that he would want to leave.It could be that he was overwhelmed by playing in a big city and prefers a small college town.
But the bottom line to all Bruins is how could he not want to play for UCLA?..it's unthinkable. Good luck to him. Maybe he will rethink his decision and come back.