Because game devs have to pay their rent.
If they go off to form their own studio, they probably have to take out a business loan to pay themselves for the time being. Interest rates are high right now, and rent and food are both expensive. It's a huge gamble to make a game and put it out on the assumption you'll be able to pay back 6%+ interest on whatever you took out. Games are not a reliable money maker. Especially from new studios.
Even if you get some sort of deal with a publisher to fund your first endeavor, there will still be strings attached to that, and publishers are pretty tight with the purse strings right now.
Which means really the only viable option, assuming you're not already independently wealthy, is that you have to work another job to work on the game in the meantime, which means it will take even longer to come out.
Bold strategy, Cotton.