If you are entirely utilitarian in how you approach making a game (as in this case) then you’ll want to create as little as possible to make the game. An existing game engine, an existing programming language, existing libraries, etc.
If your goal is the economic return that making a game will (hopefully!) provide, this is understandable.
However, how I see JB based on his past work and talks is someone who wants to spend their life bringing things into existence. From all available evidence it appears the art of creating and the art of having created is his work and his legacy. The economic return is rhe by-product, but not the goal.
We are in this earth for a finite amount of years, and he is spending his time creating new things. It’s an admirable use of time, and at least from my perspective holds a universe of meaning that working under the utilitarian approach loses.