I don’t know if that’s the case, I don’t even know if we’ve ever been visited. I’m just saying with billions of stars and solar systems out there, the idea that there is no other life out there except on one small rock seems to me to be mathematically unlikely.
Now, whether those lifeforms fly around in space saucers or are just amoebas, I have no idea.
Arthur C. Clarke postulated (in various books: Childhood’s End, 2001-A Space Oddessy, etc) that there is only a very small time window between when civilizations become technologically sophisticated and when they learn how to become G-dlike.
The former might correspond to the start of the Industrial Revolution. The latter might be when we learn to transfer our mental essence to machines. At that point, we become intelligent, immortal robots. Then those robots become sufficiently mobile that effectively become spaceships. Sometime after that, we learn how to store our mental essence in the cosmos, so we can literally be anywhere (in space or time).
When the last occurs, physical civilization has ceased to exist because we will have self-evolved to a higher level of consciousness. This transition may only take a few thousand years—certainly no more than 100 thousand.
If so, it would certainly account for why there is no physical evidence that intelligent civilizations have visited Earth. They simply stopped caring about the physical long before they could get here. Or if they do visit, those visits occur as pseudo-divine entities who use their powers to nudge evolution (both physical and social).