It depends on cases. Each post has a likes field, that store total like count for that post. It's complicated to subtract this count if some liked user is being deleted. It is possible but maybe they avoid this. The same case if an custom addon is using likes, XF cannot subtract this field for this addon (as currently) so "deleted user" is here to handle that.I was just thinking the same - if the user account is deleted, is there any need to keep the likes? Can't they simply be removed?