Haven't you seen the Terminator, it can think but it can't choose, BZ was created by Kaguya using her will, he only existed for one purpose and that was to revive her.Even a robot can think for itself,it still does'nt change the fact that the plot is essentially a "son" missing it's mother.
Its not like a person who has mommy problems, he is just a drone created to fulfill a task.
Its not like he could run around and do whatever he wanted, he doesn't possess free will like a human does.