As I understand the procedure for go-around it includes retracting the flaps.
Why is this?
The decision to make a go-around must sometimes be made quickly, under stressful conditions, like in bad weather. Retracting flaps introduces one more thing to do under sometimes stressful conditions.
Speed is low during landing and by retracting flaps you give away safety margin for lift. (Speed may also slow further since the nose is raised during go-around.)
Retracting flaps may also affect pitch and thereby make control of the aircraft slightly more difficult in a situation which may already be stressful.