If you’ve ever wondered as a pilot why you are handed back to Tower when remaining in the pattern, this is why.
3.6.2 — Pattern work must stay with Tower, and must not be handed over to the Radar Controller unless it has been decided to deny pattern work; in which case, those aircraft that are in the pattern can be converted into a radar pattern by handing them over to the Radar Controller.
If pattern work is being allowed it must stay with Tower. The only scenario when you’d be able to receive vectors from a radar controller instead is when the controllers decide they need to turn off pattern work.
Once they turn off pattern work you may be handed to the radar controller, you’ll get vectored into land, then you’d be cleared to land by Tower.
If you would like to depart the airspace instead of land, you can request departure if you are on Tower’s frequency or request flight following from Radar once you are handed off to the Radar controller’s frequency.
Reference: 3.6.2 Infinite Flight ATC Manual