Mobs despawn within ~1 chunk

this has been hapening with agressive mobs like zombies spider skeeltons the 2 vilagers i cured didnt despawn (glad they didnt l the rabbits i have also didnt but only agressive mobs i dont think this is intentional?  the video limit is 10 i tried to do as quick as possible but still wasnt enough to reduce to 10 if im not wrong they despawn in a chunk area