so you agree then that no professional game developer should make their own engine right? because their job is to ship a product.

Craft > sales. Great craftsmanship always sells, so in the long run it is not a bad investment.

If your goal is to sell a game in 3 months, sure, but not even Unreal Engine will magically turn a rushed game into a good product.

90% of the development time is making a fun game in the first place, and you’re on your own there.