Because not doing it makes most people think that there might be an update that's not being shared in order not to upset the customers.but why bother wasting time on that? If theres an update you'll be updated..
(Jojo mode) And you will say now: "But that's ridiculous! Only a fool would think that way!"
And I'll tell you that yes, perhaps, but people are fools. A person is intelligent, people are fools. Giving consistent updates even when to juts say there's no update is basic customer service practice, honed after decades of previous companies with better experience in keeping the customers happy.