We do not know that aliens haven't visited Earth. They may have visited us thousands of times. Earth is 4.5 billion years old. If aliens visited us just once every 100,000 years that would be 50,000 visits. All we can say is that aliens are unlikely to have visited Earth in the last few thousand years.
A deeper question is why haven't we seen their radio signals? My theory is that radio signals are a weak and unreliable system for deep space signalling and are only used for a centuries by a technological civilization before they come up with something better. I further theorize that the "something better" is comparatively obvious once civilizations are at the right level of technology, so EVERYBODY uses it instead of radio signals. I don't know what it is. Quantum-linked atoms? Humongous space lasers? Neutrinos?
So civilizations only use radio waves for maybe a thousand years tops, then switch to the Something Better. As a result, vanishingly few civilizations are using radio waves at any given time. Even if advanced civilizations are keeping old radio antennae around to detect new civilizations, Earth has only beamed powerful radio waves offworld in the last century or so. Unless one of them was within 50 light years, no one would have answered yet.
Anyway, those are my answers to the Fermi paradox.
This mf Lamine just received the ball on the halfway line and complained to the referee for ending the first half saying he was about to score and I actually believe him