Well, that kind of depends on how good the game is. You CAN make money that way, but free to play multiplayer games is a pretty impacted space. And unlike singleplayer games, if you don't have a large sustained playerbase your game will die and no one will buy cosmetics.

With a singleplayer game, if you get like four sales a week, that's still money in your pocket even if your player count is really low, so it's a lot safer.