Many people figure that the universe is so vast and old, it makes no sense that aliens haven’t stopped by to say hello.
What if, in the real world, aliens did turn up, and everything changed in unimaginable ways good or bad?
What if the aliens created a simulation to see what would’ve become of humans if the aliens never interfered?
If they were advanced enough to make it to Earth, they are perhaps advanced enough to build such a simulation.
Start the simulation prior to alien contact, and simply remove aliens from the simulation. Let the solar system be navigable, but beyond that is just lights in the sky and not an actual whole universe in the simulation.
Which means “we” can never see proof of aliens out there, or on Earth, because in our simulation they don’t exist!