Seems like most think that Frank is leaving because of minutes, but I have my doubts. Jesse is a foul machine and has been injured. Should be way more than 10 min a game for Frank, in fact, he average 14 min this past season. Sid averaged almost 12 min in 13 games - that's another 5 min per game that are available. And there is a good chance that Jesse leaves after next season, leaving Frank as a 1-2 yr starter.
Maybe he is leaving because:
he doesn't like the zone,
he is tired of JB's act,
he wants to go to a winning team, or
something else.