The fishing experience trophy from the event is considered the same type of trophy as the fishing luck trophy, and therefore prevents you from having both on display at the same time in your house.
I don’t understand the reasoning behind the decision from a Quality of Life perspective. Having both on display makes fishing easier to grind and more rewarding. Making it easier to grind makes it so people who don’t like it can spend less time doing something they don’t like. Making it more rewarding makes it so people who do like it can feel more rewarded for the activity they enjoy.
Having both equipped already has an attached opportunity cost, in that each will take up a trophy slot. As a result, this feels like a misguided/redundant attempt to follow the “choices have significance” philosophy New World devs have referenced in the past.