A single 1/10 factor makes it 1 trillion. 10-ish more factors and we're down to a small number of planets before we even consider the emergence of life and likelihood of propagation.
There are likely many more 1/10 factors: Habitable zone, diurnal cycles, billions of years of geological peace, sufficient water, a stable moon (maybe only one), a particular spectra of the star ...
all those were "well they seem to happen to 1/10 or 1/100 planets" individually. They cut down the space quickly when combined.
Right now the denominator is about 10 trillion.
A single 1/10 factor makes it 1 trillion. 10-ish more factors and we're down to a small number of planets before we even consider the emergence of life and likelihood of propagation.
There are likely many more 1/10 factors: Habitable zone, diurnal cycles, billions of years of geological peace, sufficient water, a stable moon (maybe only one), a particular spectra of the star ...
all those were "well they seem to happen to 1/10 or 1/100 planets" individually. They cut down the space quickly when combined.