Frequently, the aircraft offered for sale has had a recent annual inspection, so another is a waste of money on that front. Further, as has been explained by many, often, and in many places, the pre-purchase inspection is, or should be, a completely different inspection that a pre-purchase inspection. I have had no buyers that wanted to buy the seller a fresh annual inspection should something found that is a dealbreaker.
A&P's, as a group, no little about how to do a pre-purchase inspection as they have not been aircraft owners and have no clue what a potential buyer needs to know to find out if the plane is a good deal at the price requested. Mechanics, by and large, are trained to determine whether the aircraft is minimally airworthy at that moment. I don't know many buyers specifically looking for a minimally airworthy aircraft.
No one as if it passes the compression check, it can generally be called minimally airworthy. A perspective buyer might want to know if the engine is going to need to be overhauled in the first year, even though low time.
I gather you are one of the very few buyers that only care that the plane that they buy is minimally airworthy at the moment that they sign the check. Fair enough. To each his/her own.