I'd order the candidates for the basis of lifelike chemistry complexes as follows: H2O, NH3, SO2, HCOOH, CH4.
A lot of the common molecules aren't good solvents or react too readily with other common elements or molecules, like oxygen or halogens. And molecules that are good solvents just aren't common enough to dissolve much of anything.
Methane would probably only work in an oxygen-deficient environment, and ethane wouldn't form enough by coincidence to be a meaningful solvent in comparison to methane or other simple organics.
And it just so happens that H2O is very common and a great solvent, so any other potential solvent would probably have a little water in it anyway. And if it's there, a lifelike chemistry complex would probably make use of it in some way.
A lot of the common molecules aren't good solvents or react too readily with other common elements or molecules, like oxygen or halogens. And molecules that are good solvents just aren't common enough to dissolve much of anything.
Methane would probably only work in an oxygen-deficient environment, and ethane wouldn't form enough by coincidence to be a meaningful solvent in comparison to methane or other simple organics.
And it just so happens that H2O is very common and a great solvent, so any other potential solvent would probably have a little water in it anyway. And if it's there, a lifelike chemistry complex would probably make use of it in some way.