I won't argue with your main point, but a fair share of kernel devs are probably not working there voluntarily, since they write kernel code for their employer.
I'd expect that most devs capable of writing reasonable Linux kernel code would not have difficulty finding employment somewhere else doing something else.
But this is backwards! You don't become a kernel developer by being assigned to the job by your employer. Instead, employers hire people who are kernel developers. Source: I myself contributed a teensy tiny bit to the network stack loooong ago (2.4 kernel), and I worked with real kernel developers when I worked at one of the major Linux companies and for them with large (mostly US) software companies.
