Loyalty Trident belonging to a dead player will still drop an item if doEntityDrops is false
I'm sure this is just an oversight - loyalty-enchanted tridents will drop themselves as an item if they're attempting to return to a player who is dead, and setting doEntityDrops to false doesn't prevent this from happening.
Steps to recreate
-Run command /gamerule doEntityDrops false
-Give yourself a trident with a Loyalty enchantment
-Throw it, then kill yourself before it can return to you
-The trident will be found sitting on the ground as an item.