The bug

Dispensers are able to dispenser armor, elytra, mob heads and carved pumpkins on mobs capable of wearing them, such as zombies, skeletons and piglins. However, when the mob's CanPickUpLoot tag is false, the dispenser seems to be unable to dispense the equipment on the mob.

How to reproduce

1. Make sure that gamerule mobGriefing is true
2. Spawn a zombie
3. Throw an item next to the zombie, see if it can pick it up
4. If it can, dispose of the zombie, and repeat steps 2 and 3. if it cannot, proceed to the next step
5. Place a dispenser facing the zombie. Put a piece of armor, elytra, mob head or carved pumpkin in the dispenser
6. Power the dispenser. Observe that the zombie does not become equipped, and the equipment is shot out of the dispenser in item form
7. Spawn a different zombie that can pick up items, and repeat steps 5-6. Observe if it gets equipped with the equipment

This bug does not exist for the deep frozen ocean biome.

Expected behavior

The dispenser should equip the mob with the armor, elytra, mob head or carved pumpkin, regardless of if the mob's CanPickUpLoot tag is true or false.

Actual behavior

The dispenser cannot equip the mob with the armor, elytra, mob head or carved pumpkin, if the mob's CanPickUpLoot tag is false.