That's mainly the treatment plan now for HPV positive oropharyngeal cancer, Chemoradiation, and surgery as a last resort, being HPV is highly responsive to radiation, and even better with Chemoradiation. Some do a tonsillectomy before doing chemoradiation. Also, after having radiation, surgery is more difficult, have complications, and on adults there is risk of bleeding. If anything comes up suspicious on the post treatment PET/CT, usually done 3-6 months post treatment, they may remove. If they think it is still activity now, they can do an earlier scan, biopsy, and proceed from there. Doing surgery now just may be unnecessary, and would rather wait when it is.

Yours is not unusual, and is typically done. I hope this helps, and good luck on the scans.