We don't really do apple trees down here (SWFL)but you see this a lot with mangoes and avocados.In reality, the top growers do just what you are suggesting: grow out seeds until something good comes along. With their name on a variety, it is instantly in demand. Aside from sometimes tracking parentage, there is no difference between their "breeding" and anyone else.
The biggest reason people buy named varieties in my experience are time and space. They have an extremely limited area, they want the best taste, and they don't want to wait for it.
We plan on starting our groves with what is available- air layers and grafts. Once they are in production the rest will be started from seeds. There is no denying the importance of biodiversity, especially when you see what has happened with citrus and bananas lately.