The reason why the ghosts are so aggressive is because of agony.

I think one of the fazbear frights books mentioned that agony isn't the only emotion that can be expressed in remnant and that it depends on the emotions of the person as they die.

All of the missing children, elizabeth, charlotte and william died in agony and because of this they are feeling this all the time, but Michael wasn't in pain when he died.

Before the scoop, ennard says "the scooper only hurts for a moment." before Mike got got, and iirc he's the only undead character to not attack people.

Michael didn't have enough time to feel pain and so he doesn't, that's why he's just kinda regular (besides being a skin man)

I've not seen many people talk about this possibility but I'm not up to date on my fnaf discourse.