Looking at the indictments, it seems in today's mob that the vast majority of mob loansharking is directly tied to its bookmaking operations. It appears those loansharking or "extortionate extensions of credit" we see in the charges don't actually involve the mob lending anyone money but rather a gambler racking up a balance that they can't immediately pay so the "loan" is basically the bookie allowing the gambler to just pay the vig week to week, which of course typically doesn't come off the principal. It's simply the price they pay not to be held accountable for the full debt, either by catching a beating, him being exploited in some other way, or just being cut off.