So, hypothetically, if you were an advanced ET civilization and wanted to let others know of your presence --- exactly how would you do that (assuming interstellar travel is impossible or impractical)?
For starters, you would search exosystems for planets that show the capability for life... this is something that even we are just beginning.
Then you would want to target your signals to those systems with characteristics that would be most easily identifiable... i.e. a clearly non-natural signal broadcast at wavelengths that would not be blocked by their atmospheres.
Finally, because of power requirements, you would expect signals to be very short bursts fired periodically... like beacons. At the same time, you would monitor systems for beacons of their own.
So, imo, we should look for beacons on wavelengths that can be detected at ground level. And what are those? Radio signals.
What we need to do is increase our search coverage in both the sky and the radio bandwidth, and then improve our ability to find short signals.
I don't think SETI's approach is irrational or misguided... just still very limited by technological constraints.