Another thing is that if transaction is made, sellers will have to wait for long to receive payment and no seller wants that kind of delay in his/her business.
6 confirmation is the secure number of confirmation needed by a seller to accept bitcoin payment although it could be less, this confirmation time actually varies but it is not as long as we place it today and the Mempool congestion doesn’t have any effect on the confirmation time if at all you set the fee at a transaction more than enough to get into the next block
What the OP is insinuating is that; no buyer will want to wait for long before receiving payment through bitcoin after they’ve done a transaction between themselves. The transaction fees will determine how fast the transaction will get into the next block, not all sellers can wait for that and no one wants to set a high transaction fees for an amount that is not worth it.