There's a huge list of explanations on wikipedia https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_explanations_for_the_paradox https://en.wikipedia.org/

There's a huge list of explanations on wikipedia https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_explanations_for_the_paradox https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_exp...