I recognize this. 37% is pretty big here, but there are times where he is at or very close to 0%. Your BEST case scenario needs to be more than 37% to make up for how poorly you can be drawing sometimes.
Also, how is he going to play this pot other than folding? A raise allows his opponents to play perfectly against him. A call pretty much does also, especially for the guy who closes the action.
He's OOP on the turn --- and by then, his opponents will have odds to chase any draw. (That's assuming the turn isn't any diamond, Q, T, J, 9, 8 or even A) So unless he hits one of his few blanks, he can't bet. If he bets the turn, he's gonna be giving his money to better hands and building a pot on a draw heavy board with top pair. Eww.
His bet on the flop, followed by 2 callers very well defines their hands as ones which he is beating. If any player in the pot had outflopped him, they would have raised the flop to defend their hand against the multiple opponents that are in the pot.
When the BB raises all in, we have an interesting situation. The hero has to call $20 into what is now a $54 pot. Let's assume that the BB is willing to push with a pair and a gutshot (JT, KQ, etc) as well as any draws and 2 pair or a set. Well, the hero isn't in horrible shape against that range. Yes, when he's behind he's drawing almost dead and when he's ahead, the villain is very live, but look at the pot odds of almost 3-1 that he is being offered. That almost definitely offsets the times that we are behind or get drawn out on.
Since the other 2 villains in the pot flat called the bet on the flop, I am not going to give them credit for having me beaten here. I think this is a good situation to reraise all in and put pressure on your remaining opponents to fold. It's a gamble, but considering how the hand has played out, I don't think either of them has me beaten, and if I push here, they are not going to get good odds to draw to a hand that beats mine. If i get them to fold drawing hands that would have beaten me, I increase me equity in the pot. I'm willing to gamble that neither of them has a hand to stack off with, and I'll take my chances heads up with the villain in the BB when the pot is laying me 3-1.