i don't have experience nor i know how to manage a studio but how did the 90's and 20's studios survived ?
what is required then if different from now yes but still the same concept right?
You have to differentiate between something being possible and that something being easy or within reach of anyone.
Running a video game studio is not easy, especially in today's demanding market. That does not mean that it is impossible, but rather, that it is a field that requires a lot of skill and that is not available to everyone, it is not enough to say I will make a video game today and tomorrow I will have a video game studio, even if you have a very successful game.
People who have a moderately successful game do not invest in moving to a studio for two main reasons, personal decision and economic factors.
As I told you before, just because you like it or know how to make games (and have a successful one) does not qualify you to be the leader of a development team, there are different skills involved.
This does not mean that it cannot be done, but rather that it is not for everyone.
The economic factors, as I told you, the cost of keeping a video game studio operational, even a small one, is very different. VS the cost of creating your own video game without paying salaries, rent, etc.
A studio must function like a business, that is, it must produce enough product annually to pay its costs and make a profit. If a game is not successful, you still have to pay salaries, rent, additional staff, such as lawyers or marketing, etc.
Many people don't want to get into managing a company (with all the complications that that means), and are only interested in programming or creating art for a video game.
And you must be aware that creating a video game company, even if you already have one or two famous video games, will not be a guarantee that you will get more successes or that you will even be able to pay your costs.
Again, I'm not saying it's impossible, but it is something complex, requiring many different skills, and not something for everyone., and You're not asking how a video game company can survives, you're asking why a neighbor's son who managed to make a relatively successful game doesn't start his own company. Or so I understood from your question.