They don't care about your headcount, but you do use more service.
You can be against licenses, because you think it should be possible to own software. (I agree somewhat with that.) But when you accept a fee for usage (aka. a license), the vendor gets to tell you the pricing units in which the usage is determined. Expecting the same cost while changing the pricing unit, isn't likely to be accepted by the seller.
Don't like it? Build your own transnational ERP. /s to be clear.
The question is rather whether a single type of subscription license makes sense (e.g. when AI burns through more resources than the average human, should the subscription go up for everybody? - as a human I would be pissed to subsidise heavy AI usage by other users).
E.g. there should probably be special 'AI licenses' similar to how some products have special 'CI licenses'.