It would be interesting to see what the motive behind boom AAR was for the P8 or is it a case of that is what the P3 had.
USN P-8s, like USN P-3s fly lots of places where there is no USN presence. There's no way USN is going to deploy a carrier or carrier aircraft to support a P-8. So USAF has the responsibility to provide tanker support, and USAF has mostly boom tankers. As for the P-3, it has zero inflight refueling capability.