Plus teams like Miami might expect to get more out of a player, since they've already got the structure in place and have the incentive of a possible championship run, the way that the Patriots have sometimes gotten better effort from "problem" players in the past. Not saying it would happen, but I'd expect it to factor into their thinking, as it probably did with bringing back Beasley.
Plus, Bynum's seven feet tall and not dead. How many chances did Tskitishvili get back in the day? Hasheem Thabeet? Bynum has (limited) time as an actual good NBA player on his cv, which gives him a leg up on those guys.