Remember that to prevail in a liability action one must prove that he/she has suffered harm or loss. Without specific knowledge that one has been wiretapped, how to prove the cause of any harm? And imagine the revelations of exactly what folks were discussing that caused them harm when they were monitored. I believe the suits are designed to learn of the methods the intel agencies are using, to embarrass our officials and only secondarily, to protect individuals.
Additionally, from what I've read, the wiretapping effort is primarily an attempt to determine patterns of phone calls between individuals and foreign persons, which patterns could lead to actual call monitoring for content.
On the second part you are very correct. Much of the sniffing is pattern recognition and associated AI that goes with that.
As for the first part, some of that is circle logic. IF folks did not know they were wiretapped, we can assume they did not sue [as they would not know to sue].
As for proving harm or loss, Courts have held for years that illegal searches are subject to suit, turning over personal records without authority to do so has civil ramifications. This is no different.
Again, one of the primary issues in this bill is precedent. It further takes away a right of privacy and starts an erosion that is hard to stop.
I am for stopping terrorists as much as anyone. But if we can't do it from the confines of our laws and Constitution we really need to reassess what we are as a country.