I feel like a good deal of payment processors and merchants go by the route wherein the payment processor instantly converts the BTC to USD before paying the user.
This then eliminates the benefit of trustlessness anyways.
I guess if you assume merchants that are looking for payment methods wherein they keep the Bitcoin in the end, the trustless nature can "kinda" help. But if you already don't trust the payment processor, it seems like you would just set up your own system, especially if you're just having to listen to a single address, and not needing instant USD conversions as well.
(And as others have noted, the fee does not really add up when you consider the existence of bulk transactions)