"Even then, the wobble is detectable only for giant planets, which are those about as big as Jupiter.."
So what does this tell them about the existance of earth-sized planets? Zippo.
In all the millions of galaxies, each with millions of stars, its hard to believe that whatever conditions were conducive to the formation of life here did not also occur elsewhere.
The condition for the formation of life is everywhere in the universe. Indeed it transcends the universe. It is God's creative power. Someday soon you will come face to face with that power.
Moreover, I think that we can only find Jupiter-sized planets if they're orbiting really, really close to the star. Since we don't have any gaseous planets next to the Sun, it stands to reason that the only planets we can find right now are the onest that have been formed in a different way. Bottom line: we simply don't have the technology to detect planets like any planet in our Solar System.