I believe the existence of extraterrestrial life is nearly a mathematical certainty. While our own existence is exceptionally improbable - whatever system led to the rise of life on our planet almost certainly would have generated similar results, elsewhere.
Now... whether or not it is flying around above our heads.... I don't know.
Logical arguments can be given for why they would not be expressing what we interpret to be attempts at contact.
One of which I've developed and have been rather partial to (since it departs from alien worshipping tendencies): We are more advanced than them.
That might sound silly... but ability doesn't necessarily translate to capacity. If we accept that modern accounts of flying objects tied to ET activity parallel historic examples... we can conclude that not a whole lot has changed for ET, technology wise, for the past 30,000 years (cave paintings and oral history predating written languages tell of wars fought amongst gods in the sky). The same can be said for us... kind of. Agriculture took off - and it's been exponential growth since then. Metal working advanced hand-over-fist and the steam engine coupled with electricity drove us into cubic growth rates. 100 years ago, we were just getting the hang of electricity. Or so the alien scouts reported.
Then, two decades later, they pick up gamma radiation spikes and we're nuking things. Vacuum tubes are everywhere (possibly a novel technology to them - something lost to their own history or possibly never developed by their species/coalition).... then someone gets the great idea for a transistor based on this 'quantum mechanics' thing...
And here we are, today.
We just went from considering them gods to having a glimpsing how their technology might function within two generations.
If there are aliens watching us - we're probably turning some heads.
And that -might- be why they are being more cautious. It's not like we need to be given any hints on how their technology works. We'll have their shit reverse-engineered before they get done figuring out how we reproduce (since that seems to be a popular field study for them).
Of course - we could also be some kind of experiment or 'problem solving' contingent... kind of like how we evolve bacteria to perform certain functions by controlling their environment - perhaps we are part of a larger network intended to solve various technological problems that would be difficult for a species/culture with established doctrine to develop.
But - that all bases on the assumption that ET knows we are here and has been visiting much at all.