It's handy if you run a service and the internet runs clients you didn't write to access said service. (or vice versa)

Also handy if the internet is running a DDoS reflector and you're being targetted.

Otherwise, usually no sense of urgency for fixes I did for me/my employer and want the rest of the world to benefit. My problem is solved now, everyone else can get it when it ships.

Running a fork is a lot of work. You need your fixes upstreamed so that you don't need to backport other people's fixes