Space is big, signals are weak
I would think that all but directional signals specifically sent towards us would be too weak for the SETI to detect and, in any case, high power broadcast signals would probably be used for a very brief period in any civilisation as they quickly move to more efficient low-power directed and coherent beam transmission.
Furthermore, they would probably switch to digital equally quickly and then start encrypting everything routinely, for commercial reasons if not for anything else. And a well encrypted transmission looks pretty much like random noise.
So, the chances that there is a civilisation that is going through their momentary high-power analogue broadcasting phase and that is close enough for us to detect them and is using the frequencies the SETI is listening to are very very slim even if, otherwise, there are millions of inhabited star systems in our galaxy.