It's not a bullshit reason. You can put all the lipstick you want on the pig and put software all around it to make it all sorts of easy, but at the end of the day, having to reboot is a stop-the-(machine's)-world situation. Not having to do that is just better. Even if it doesn't work 100% of the time, that's still better than having to reboot the whole fleet. 45 days to reboot the whole fleet!

Throwing FUD and saying disaster is looming because its scary computer magic (out of MIT) was a scare tactic RedHat used to throw around about Oracle/Ksplice until they developed their own (Kpatch), then suddenly their sales team had to backtrack and say actually hot patching is good and can be trusted. I'm not saying it's not risky or dangerous, it's operating in kernel space, but that's why they pay really smart people to be careful when doing it, and not digital equivalent of a plumber who can't do more than glue libraries together.

A better understanding of the underlying technology so it's less magic might assuage your fear of it, but thinking Facebook is so dysfunctional that they haven't already made it easier to reboot is to misunderstand the problem at hand.