I think I solved it.
Imagine that there was an alien technologically advanced civilization in out galaxy before us.
Chances are high that they would have been around for around a billion years already.
That is plenty of time to colonize an entire galaxy even at a mere 100mph.
But we don't see such a reality, right? Hence the Fermi Paradox.
BUT, think about the reality if that DID happen?
Would we be here?
No!
We can only exist where such an event did NOT happen.
Therefore:
We exist, therefore we are alone in the galaxy.
(Most likely.)

There's also other theories, like how technological civilization is just too rare to occur twice in a galaxy.