Or they are true but we are the first to reach this technology level.
Now, you could make the same argument about evolution. Bacterial evolution is far quicker than human evolution. If they saw an advantage to killing humanity, we'd be dead before dinner. So why haven't bacteria killed us yet ? No advantage ...
The simple truth is: it's not worth it. Large bacterial species lose and gain more biomass on a daily basis purely through accidents than all human biomass combined, and they wouldn't be able to use all that biomass if they took it from us, nor would they be able to harness the energy humans use, so that's no good either. So it's an idiotic thing to spend energy on, and so they don't spend energy on it.
For space faring civilizations you can make a similar argument. Despite the movies, there is nothing on earth that is worth coming down the gravity well (especially not water. There is FAR more water in the asteroid belt, and it's far easier to collect and use), and maybe it goes so far that it's just not worth it to come into a yellow dwarf solar system : there'll be exponentially more materials and energy available in many other solar systems. So at the very least, we'd be last in line for a visit, and maybe just outright not in line at all.
Reality is that humanity will never leave earth, and AI will never return home. We will launch AIs, and they'll decide to venture out, and conquer and multiply in starsystems with huge stars, massive asteroid belts (lots of resources ... no gravity wells you have to spend energy getting into and out of).
Why haven't we seen aliens ? Same reason bacteria don't kill us (well, only by accident) ... we're just not worth their attention.
And would they do it to study biology ? Well, you'd have to take into account that any race hopping solar systems we wouldn't be the first race they meet. Or the 100th. We'd be the 10000th. So would they still be interested ?
It's also entirely possible that amidst the vastness of space, we have yet to even be noticable, much less noticed. What few traces of our civilization that have been leaking into space for merely a century might be unrecognizable from background noise and impossible to to trace back to us if another civilization just happens to come across it.
Maybe they were listening for millions of years, when there were only dinosaurs here.
It is statistically improbable for you to win. Given a large enough pool of players, statistically someone has to win.
It's incredibly unlikely, but the chance isn't 0. Someone has to be first.