I think it's just that mafiosi didn't go to jail that often, at least never for a long time back then. If there was a RICO law in the 40s and the 50s, I think many would have turned informants even at those times.

Willie Marfeo to Henry Tameleo:

1) "You people want a loaf of bread and you throw the crumbs back. Well, fuck you. I ain't closing down."

2) "Get out of here, old man. Go tell Raymond to go shit in his hat. We're not giving you anything."