I disagree with your starting point, almost all successful games (that I know) tend to outsource, for example, if you are a programmer, you pay for the art, that way the game improves the quality, but you are not tied to paying salaries or assuming the game studio maintenance costs
Making a game is not the same as managing a studio. Just because you know how to make a game does not mean you have the necessary skills to be the leader of a game studio.
A studio with hired people has fixed monthly costs that are not minor. A single successful game is not capable of maintaining a studio over time.
Having a successful game does not mean that you are going to release a second or third that is successful, there are many, many studios that have had one or two successful games and then have closed because they have not been able to make enough money over time to maintain the costs of the studio.
There are several examples of successful games that have sold well, but if you analyze them, they would barely have been able to cover the costs of a small studio.
I would say you are wrong to undervalue the costs of a game studio. The video game market is a very complex and competitive market, creating better quality games does not mean that you will sell more. You can invest all your profits in a second game, which has a much higher quality than the first and still not sell even half of it.
There are a few examples of very successful games that have allowed successful game studios to be created over time. But there are many and I mean many more examples of the opposite.