Why does the app ask you a question and then the OS asks you the same question?
E.g. the app asks if you want to turn on notifications, and then when you say yes the OS also asks if you want the app to turn on notifications.
Because the OS can't trust any of the software in "userland" to not be trying to cheat.
The OS has to show UI it trusts, that it knows shows the user relevant information to allow them to make an informed choice.
What if you could make it so the userland UI could be trusted in some cases?
You'd remove all of the obnoxious permission prompts; your common sense, obvious actions in the app would be sufficient to let the OS know you consented.