It was too easy for one state’s congressional delegation to hold out for a special concession in any tariff negotiation, and then when the amended version came

It was too easy for one state’s congressional delegation to hold out for a special concession in any tariff negotiation, and then when the amended version came up to vote, another state would do it, and then another. So Congress gave the president unilateral power to set tariffs, which also is better going into a negotiation since the other side knows you can deliver whatever you agree on.