I once had the strange experience of playing such a game. It was an "instant game" on Facebook Messenger, that simulated a slot machine casino. It didn't have a cash-out, so it was really just a game.

It had an auto-play, so I watched the dials spin and lights flash until my money ran out, and it prompted me to buy more.

The game played entirely by itself, until it inevitably lost. It ran with no meaningful player action other than selecting which slot machine and buying coins.

And it had a leaderboard, with Facebook profile photos and names of big winners that I can only assume spent real money to be there.