The uncovered alien worlds do not have rocky surfaces or breathable atmospheres. They are similar to Jupiter, which makes them inhospitable to life. Taking pictures of exoplanets from the ground is difficult, verging on impossible. Still, astronomers hope to see from the ground a few really giant planets located at moderate distances from their sun. The search for Earth-like planets is restricted to only a fraction of the Milky Way with current technology.
Astronomers are able to look in detail only at the sun's closest neighbors.
Suppose we send out an instrument to look for Earth-like planets and we give it 70 years of observing time. It will take it about a day to observe a particular star system to find whether it has an Earth-like planet. At this rate we might survey perhaps 25,000 stars, a tiny bit of the Milky Way Galaxy, which contains about 10 billion stars. There could be 'billions and billions and billions' of Earth-like planets out there, and we would have missed them all. Our only hope is that Earths are extremely common.