Question

Why would Esterification of a carboxylic acid on a molecule increase its solubility in THF?

Answer 1

The main principle of silubility: like dissolves in like.

Carboxylic acids are polar molecules, moreover the can form hydrogen bond with water molecules. They tend to be soluble in polar protic solvents like water.

Esters are polar molecules too, but they can not form hydrogen bonds, they tend to be soluble in polar aprotic solvents like THF.