> This struck me as a potentially mind-blowing win for NetBSD. Why isn't every RTOS, embedded system OS, toy OS,experimental OS etc. based on NetBSD?

I think it is used a lot as a starting point for porting other OS, but it doesn't necessarily persist.

Supposedly Apple started with NetBSD when porting OS X to x86, not that x86 is exactly esoteric, but NetBSD lends itself to being a starting point. From what I read nothing remains of NetBSD in OSX, the current BSD userland is from FreeBSD but is pretty old still.