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.
What? There are many recreational (small) drone rules with the FAA because they can harm people. A 6 foot drone falling hundreds of feet on someone is obviously a threat.
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.