I’ve seen quite a few short sales in the last few years (including 1-2 recently) that immediately went onto MLS as contingent. Broker lists them under market, gets a “friend” to make an offer, friend buys it and flips it for 1.5x the price a few months later, gives broker a kickback.
Unethical and illegal as hell, but real-estate is a crooked game.
As far as regular sales, if the broker can find a buyer at an acceptable price before it goes to MLS, why wouldn’t they save the MLS listing fees?