Quoc: "Why Did n't I Think of That" is a song written by Bob McDill and Paul Harrison, and recorded by American country music singer Doug Stone. The song reached the top of the Billboard Hot Country Singles & Tracks chart. It was released in June 1993 as the fourth and final single from his CD From the Heart.

Who sings why didn't i think of that?
HW Chung: OK, some thoughts:
The relevant sentence in the passage is: "Why Did n't I Think of That" is a song written by Bob McDill and Paul Harrison, and recorded by American country music singer Doug Stone. The answer is American country music singer Doug Stone.