[nine_k]

There need not be any nefarious intent. Just being around a civilization which is much more advanced is risky: if they operate nearby, they can hit you by mistake or negligence, and whatever consequences are tiny for them may be significant for you. They can just see you as a nuisance and want you to stay sufficiently away, no matter what your opinion is. Think about an anthill near a human settlement. (Don't think about a wasp nest near a human settlement; may be too depressing.)

[mkr-hn]

From Babylon 5, a quote from G'Kar:

>> "There are things in the universe billions of years older than either of our races. They are vast, timeless. And if they are aware of us at all, it is as little more than ants…and we have as much chance of communicating with them as an ant has with us. We know. We've tried. And we've learned we can either stay out from underfoot, or be stepped on."

https://www.youtube.com/watch?v=ZLZW8Deq8vE

[Izkata]

> if they operate nearby

I think my favorite variation on why we seem alone was how Earth exists in a space version of the Bermuda Triangle, called the Veil of Madness, that all spacefaring civilizations avoid: https://creepypasta.fandom.com/wiki/Mankind