A good single-player game can make money by just being good and worth the price, absolutely. Too bad these are live-service games that need to somehow convince you to give them even more money once you've paid for the game once. Most players fall into the category of "I paid for this game already, they got money from me, I'm not giving them more", and that's how games die.

Live-service games need other ways of generating revenue, and without subscriptions, it's down to either microtransactions or paid content expansions. As I said earlier, subs aren't really a viable option in 2021 anymore, so it's tougher to strike a good balance.

For MMOs, paid content expansions in an otherwise B2P game is a very bad idea. There's a reason it doesn't really happen in multiplayer games anymore - it used to segregate the player population too much and would contribute to a feeling of the game 'dying'. There's nothing worse than wanting to play a game with your friend, only to find out you actually have to pay even more to access some content that's not included in the base game. Guild Wars 2 does this model and their revenue reports are almost like a warning to other developers considering that model lol.

Microtransactions are sort of the default, and when done well, don't take anything away from a game being good.