Here’s an alternative “Zoo” hypothesis regarding a solution to the Fermi Paradox. We’ll call it the Lab Hypothesis.
If you’ll recall, the Zoo Hypothesis is the idea that intelligent, space-faring cognizants exist and they, either a single species or a collective, have intentionally isolated Earth (we’re effectively quarantined) in order to allow humanity to sink-or-swim, as it were.
The Lab Hypothesis is similar, however, the determining factor is that outside intervention is not forbidden, only restricted. And that Earth is “mined” for the myriad lifeforms and organic compounds and molecules that are produced by those lifeforms.
Think, autonomous chemistry laboratory, which haphazardly creates and/or evolves millions of chemicals which are rare in the galaxy. These fabrications are collected by aliens (which might explain the errant sightings of spacecraft), and then sold/traded/used by other populations of intelligent races in the galaxy.
Consider that life is rare (so far — very rare). And that life itself is more capable when it comes to producing strange new chemicals. Even the most advanced AI-computers in the galaxy cannot calculate the working, stable combinations of elements that make up, say, vanilla, cinnamon, coffee, banana, okra, or cannabinoids, millions of chemical and drug compounds the corp-pharma industry searches for in the jungles of the world.
Life, nature, is just too good at making stuff up that works, on some level, to affect living beings, psychotropically, physically, or materially (spider silk for example).
So, Earth is a lab, and we’re lab-rats, and the thousands of spices, fragrances, liquids, intoxicants, etc. that we enjoy — our alien neighbors do too.
But they want to keep it a secret — and not risk polluting the petri-dish.