It's easy to say they're probably no threat. The number of ways for something to be a threat is much smaller than the number of ways of something being a not a threat, therefore the probability of them being a threat is very low.

It's always possible to make a just-so story about them being a threat, and those are the kind of stories that catch people's attention. The odds are they belong to a mapping company, or a drone construction company, or a university or something else completely innocuous.

Why don't we know? Well because it's a big world, and people dealing with actual problems have more important shit to deal with.