>>11280000A couple of guesses:
Selfish reason:
We are entertaining like a zoo.
We serve no purpose to them and are uninteresting and also not a threat.
The value autonomy highly and don’t want to interfere with our choices.
Utilitarianism:
They don’t think we are ready to know of their existence because we are still too dumb. We have wars and eat meat. Maybe they don’t trust us with alien technology that could be used for deadly reasons.
I’m an ethics brainlet whose only exposure was engineering ethics for my degree but pretty interesting to think about.