Why is the water solubility of CO worse than that of CO2?
The fact that $\ce{CO2}$ does not have a dipole moment does not really mean it's nonpolar.  What $\ce{CO2}$ has is a quadrupole, two opposing dipoles that occupy different portions of space (opposite sides of the carbon atom).
Ordinarily we expect an electrostatic interaction with a quadrupole to be relatively weak, but in $\ce{CO2}$ the component dipoles are strong and at close range the water molecules can &quot;home in&quot; on one end of the molecule and interact selectively with the corresponding component dipole.  Thereby the electrostatic interaction between water and the $\ce{CO2}$ quadrupole is stronger than the interaction between water and the weak $\ce{CO}$ dipole.