Now in 2021, with our discovery of exoplanets and deeper knowledge of astronomy, the vast number of Earthlike worlds doesn't seem as possible.
There seem to be planets around the vast majority of stars, and many planets in the habitable zones of stars. Major impediments include:
1. Most stars are red dwarfs, and most red dwarfs are unstable flare stars
2. Most planets don't have a significant electromagnetic field
3. Few, possibly extremely few, planets may have plate tectonics, which may be vital for habitability.
But the jury is still out on the frequency of life-supporting worlds, they could still be fairly common.