Simple? change; when you double click an item in a gear slot it should equip that item. Just now nothing happens which makes it different from double clicking an item in your inventory. An “equip” menu opion should also be added since not everyone double-clicks and again makes it consistent).
One need for this is say you want to switch your weapon to something that’s in a gear slot, but don’t want to equip that entire set (e.g. you are doing Season activities, want to switch to your Angry Earth axe, but it’s in one of your gear slots).
What you have to do just now is drag the item from the gearslot to the equip it (again inconsistent UX, you can drag to equp, but not double-click). However if you miss when dropping the item it’s now un-equipped from your gearslot and you have to find where it is (inventory, anyother gearslot etc).