Should online shops present their payment transaction costs transparently?

Why don't online shops display their costs transparently so that customers can make an informed decision? The will to become more independent of the USA in the financial sector is greater than ever. Large shops like Otto or something like that could even start reward programs in which part of the saved transaction costs go to the customer. I just had a very long list from which I should choose a payment method and since it is a small shop, I should have