I just don’t think they have the wherewithal to travel here from wherever they are.
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The thing about Aliens is they are Alien.
You can only measure what you imagine is possible by our standards and knowledge. But we cannot measure what their standards and knowledge make possible because we are not them.
The may have come here millions of years ago, or they may be able to jump from on spot in the universe to another just by stepping there, as postulated by James Clerk Maxwell, the man who gave us everything we know about the entire electromagnetic spectrum.
Hope not. It's all fun and games till the Wraith or the Goa'uld show up.