Because that would be a pull and not a push.

Not that there is anything wrong with that, and in many use cases it would be a fine alternative. But sometimes you really do need to push data to the user even if they aren’t polling for it.

Pill reminders would be something that you’d want to push. You can’t be sure the user is running your app (even in the background), and the actual state changes are rare. So some kind of mechanism where the client doesn’t initiate the check would be better.

Using a long poll for email or slack or something like that can make more sense in some scenarios.