No, it's an actuarial model. Priority Pass is owned by an insurance company. They know how to set the cost of membership (individual, corporate or bank sponsor) to recover their costs based on average usage projections. Individual usage isn't very important if the number of members is large.
Priority Pass recently increased the published guest fee from $28 to $32. Even if you do not pay the guest fee because your membership includes two guests per visit, it tell us that Priority Pass is likely raising the price they charge banks for these memberships.
I speculate that Priority Pass is offering different reimbursement rates to restaurants than to lounges, and likely not the same rate to all restaurants. The restaurant aspect of their business is new, and they will be testing different arrangements.
That makes sense. So you mean the cost incurred by each visit is mainly covered by the bank? For some reason I always thought banks only give PP a flat fee, but I guess that could be wrong.
In that case, since I have multiple PP from multiple banks, maybe I'll try splitting my lounge visits between different cards.