Before, you had multiple redundant methods in 2 classes. That's bad for cleanliness and maintainability. Now you have 1 manager, which you can add to multiple classes, without redundancies (if you remove the remaining 2 unneeded methods). That way you can "make" things gatherable by adding the manager to it. However, having it on Entity implies that every Entity is gatherable, which is obviously wrong. For 100% clarity some people would make an Interface for this I guess, "IGatherable"... but you don't have to do that.

Technically even having it on MabiCreature is wrong though, because not every creature is gatherable. But putting it in prop, npc, and pet makes coding the skill more annoying.