An overlooked factor might also be the lack of (habitable) solid surfaces in the cosmos. There exists an interesting XKCD comic "Surface Area", about a giant

An overlooked factor might also be the lack of (habitable) solid surfaces in the cosmos. There exists an interesting XKCD comic "Surface Area", about a giant patchwork quilt, comprised of all solid surfaces in the Solar System. To visualize that the combined surface area of all solid bodies (in the Solar System) is surprisingly small. https://xkcd.com/1389 https://xkcd.com/1389 Earth and Venus had a major share on that quilt, and the combined surface areas of all other planets, dwarf planets, big moons and small moons were surprisingly small.