What are your theories on why Aliens haven’t invaded earth yet despite visiting our planet?

So as far as we are concerned aliens haven’t invaded earth. I know it’s a stupid question to ask, but what do you guys think as to why they haven’t invaded earth yet? Even the hostile aliens don’t seem to find any reason to destroy an inferior race, so maybe there was either a treaty that was signed with other alien races to not hurt the earth and humans or they see humans as a valuable resource that they decided to let them live.

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