The first problem I've always seen with the detection system they are using to find alien planets is that were really not providing any real tangible evidence of these planets actually existing. My understanding is that they're looking at the periodic wobble of a star, and from that they are deducing by math what planet or planets are orbiting them. There is no way for them to actually take a real photo of a planet - not even the Hubble can really do that.
So what happens if their calculations are wrong? Math is concrete, but the people behind the math can make mistakes. Physics is an evolving science.
Also I've never read anywhere anything on the calculated accuracy possible with these measurements. What I mean is that if an Earth sized planet existed in the system being measured would the wobble be great enough that we could detect it? This provides some insight:
“I have a problem referring to our own solar system as unusual, because we haven’t done that experiment yet, we haven’t searched for our own solar system yet,” said Turnbull Thus far, the kind of data obtained and the type of observations made are tuned to search for Jupiters and not Earths, therefore that’s what we find. “The experiments were designed for that,” she explained.That's what I thought. How do we know that Aliens aren't looking at our own solar system and seeing a couple giant gas giants we call Saturn and Jupiter?
That being said, I do think Earth is rare. Most scientists know it is. My guess is that there is life out there, but the distances are a lot farther than a few systems next door. If they were next door you'd figure we'd be picking up an alien "I love Lucy" by now.