If you look more a bit more closely, you will notice that the kernel developers' goals are vastly different from what you think they are. They want to build the best kernel possible. Everybody who wants to contribute is welcome to submit patches. Some will be accepted, others rejected, names called, and so on. In the end, the kernel will be better and/or people will have learned from the experience. However, companies that provide only binary drivers do nothing to advance the Linux kernel. Some kernel developers consider binary drivers a violation of their copyright even.
Cooperating with proprietary vendors gives the Linux kernel developers nothing in return, just letting others exploit their work for free without giving anything back.