One argument that life is common is that life appeared very early on Earth, and so by inference Origin of Life is likely to be an easy process.
But there's another possibility: perhaps panspermia is easy in the dense star cluster the Solar System formed in, which packed 1000 or more stars into a cubic parsec. In that case, if life originated early, it could then spread to all the other star systems in that cluster. This would amplify the statistical weight of "early" OoL. Most planets on which life gains a foothold would be those in which OoL happened to occur in this birth nursery, and then spread.
This concept has interesting implications for SETI and science fiction. Life might be extraordinarily rare or absent elsewhere in the universe, but there may still be thousands of other systems in our galaxy that were seeded along with ours. They'd be spread out now around a ~180 degree arc around the center of the galaxy.
But there's another possibility: perhaps panspermia is easy in the dense star cluster the Solar System formed in, which packed 1000 or more stars into a cubic parsec. In that case, if life originated early, it could then spread to all the other star systems in that cluster. This would amplify the statistical weight of "early" OoL. Most planets on which life gains a foothold would be those in which OoL happened to occur in this birth nursery, and then spread.
This concept has interesting implications for SETI and science fiction. Life might be extraordinarily rare or absent elsewhere in the universe, but there may still be thousands of other systems in our galaxy that were seeded along with ours. They'd be spread out now around a ~180 degree arc around the center of the galaxy.