The Fermi Paradox is the most profound measurement in the history of Darwinism. If intelligent life is so easily produced by evolution then why do we see zero evidence of alien intelligence?
Intelligent species never build self-replicating exploration craft. They never build galactic scale artifacts. They never exhibit visible advanced technology. They never build berserkers. They never develop FTL spacecraft. They never reveal any evidence of their existence. They never remain corporeal long enough to be detected. They never survive their nuclear age.
99% isn't good enough, the universe is too large. If 99% of species don't survive their nuclear age then 1% do and we should see some of those 1%. That's what so many proponents do not understand. 13 billion years is a very long time for the 1% to populate the Milky Way with robots or spaceships or colonies.
Even my preferred explanation uses never: There never has been a 2nd intelligent species.
Here's an answer to the FP which does not need the word never. Intelligent life is rare, and it did not evolve in any galaxy until about 1 million years ago. In this case no species has had time to send out exploration craft far enough for humans to see them. There might be 10 or even 1000 intelligent technological species in the Milky Way. But if they are all young species then we won't know about them for millennia. I can't explain why intelligence only arose recently, but neither can I explain the Fermi Paradox.