Our ability to detect signs of ETI is very limited. It could be all over, and we could have even detected it already, but we don't realize it. Studying up on astrophysics (how we detect and transmit signals, how signals attenuate and fade over cosmic distances, and some of the signals SETI has already received) reveals that.
The Fermi paradox is only a paradox due to the assumption that in a few million years a civilization will colonize the entire Milky Way just because it's theoretically possible, so we should be up to our eyeballs with aliens' von Neumann probes. But many things are theoretically possible. We could build the world's largest house -- the size of Nebraska. Every nation could reorient and sink their economy into that megaproject and do it. But it's irrational to; there's better things we want to do with our resources (which will always be finite, all the way up the Kardashev scale). That's why I think it's silly to expect any intelligent life to be that ambitious (or competent).
The Fermi paradox is only a paradox due to the assumption that in a few million years a civilization will colonize the entire Milky Way just because it's theoretically possible, so we should be up to our eyeballs with aliens' von Neumann probes. But many things are theoretically possible. We could build the world's largest house -- the size of Nebraska. Every nation could reorient and sink their economy into that megaproject and do it. But it's irrational to; there's better things we want to do with our resources (which will always be finite, all the way up the Kardashev scale). That's why I think it's silly to expect any intelligent life to be that ambitious (or competent).