I personally always enjoy Meta update posts on other instances to see what they're up to, how they handled a particular problem, or offer help if they need it, and welcome the same on the meta posts on my own community from non-members.
because it affects the communities too, lots of outside accounts use the communities here
if there's downtime for the instance or database issues or something, then subscribers to c/programmer_humor or c/programming might want to know because it affects them too