We might not recognize a signal even if we were looking right at it. For example, an analog AM or FM carrier stands out way above the noise, but digital broadcasts make better use of bandwidth and are thus more noiselike. A highly exploited bandwidth would be indistinguishable from noise.
There may be a window of only a hundred years or so in which a civilization is advanced enough to put out a detectable signal but not enough to make full use of bandwidth.
Indeed for the present. However, to communicate across the solar system we will require higher-powered carriers. So there may be a temporary lull instead of a total lapse of high power carriers as we expand thru our solar system. All SETI is doing is looking for that CW carrier. We are not looking for information at all.