Personally, I think you're neither harsh nor realistic .
Feedback is completely voluntary for both parties, but you will find most sellers will take on this ' unwritten rule' , that is, to leave feedback only after the buyer leaves any.
The reason for this, because a seller can only leave good / positive feedback, leaving that first, the buyer can turn into the buyer from hell, and positive feedbacks cannot be revised.
Far better to leave the seller some feedback it is meant to describe the fulfillment of the transaction, you may well find then to receive a seller's feedback.
As above, it is voluntary most members do not leave any, and there are 60 days in which to leave some. Also, some sellers do wait until a certain period passes to leave a bulk feedback.
@middxdecor