It's probably more to do with personality type than intelligence or anything else. It takes an extremely thick skin to handle the regular patch review slating dished out by most of the core team.. I simply don't want to deal with that shit for a hobby, and it'd take an impressive salary to make me deal with it professionally.

There's being opinionated, then there's being an ass, and I think there's far too much of the latter on the kernel lists.

If you look at the modern nerd, compared to the generation that birthed the kernel, they're more socially aware, fashionable animals that are more interested on working on sexy, visible things. Why spend your day dealing with bad attitudes and timing bugs when you can pick up $200k+ writing Ruby apps that enable sharing 5 second video clips?

I doubt the kernel will ever be starved for new talent, just that the ratio of people willing to work on it or deal with the social norms it entails is shrinking all the time.