The reason for this is that water can be solid, liquid or gaseous at typical earth temperatures. Only the vapor has a greenhouse effect. Most water vapor quickly condenses to a liquid or freezes to a solid, rain and snow. C02, on the other hand, only exists in the gaseous form, the greenhouse component. C02 CAN dissolve in water, though, and that is indeed one way of removing it from the atmosphere.

I suspect these characteristics interact in very complex ways with one another, but the final result is that carbon dioxide plays a much bigger role in greenhouse related temperature excursions. Modeling the effect of particulates, which may come from volcanoes, industry, or fires, tend to reflect sunlight back into space to further complicate the issue. Conversely, when those particulates settle on ice, they tend to absorb more sunlight!

There are other issues, too. AGW creates heat, which creates evaporation, which creates more water vapor, which creates clouds, which also reflect sunlight back to space. How all these effects work together, and both the interlocking positive and negative feedback loops they generate, is very hard to model.

That’s why I stick to easily measured phenomena that reveal to us the combined effects of these processes, like polar ice cover and average temperature of atmosphere and ocean. That requires no a priori assumptions like models do. You just deal with a simple easily measurable physical quantity.