Am I doing something wrong?
I’d guess this is caused by you locking your PvP trinket (Sinister Aspirant’s Medallion) indicated by the orange padlock icon in front of the item name. That item is probably worse than the alternative (your 410 Galecaller’s Boon) which can’t be used because you locked one trinket slot.
Overall those changes would be necessary to give you the optimal result if you absolutely want to use your PvP trinket but that result would be worse than your current gear.
You can unlock that item by either clicking on the padlock icon or by using the “Unlock All” button in the bottem right.