In terms of molecular motion, why does an increase in pressure lead to an increased solubility of a gas?

 We imagine a piston cylinder and a solution of gas and water. Molecules are in constant random motion and some of the gas particles are in the vapor phase while some in the liquid phase. At a specific volume, molecules move freely. However, when the piston is moved down, increasing the pressure, some of the molecules in the vapor are pushed down to the liquid phase in order maintain equilibrium thus increasing solubility 

Temperature and pressure