Why are negative feedback loops used to control body homeostasis?

(Short answer)

Homeostasis is defined as the state of body in which body maintains several chemical and physical changes inside the body affected by external factors.

Negative feedback loop includes a sensor, stimulus, control center, and effector which is used to control homeostasis.

A negative feedback loop is a reaction that reduce an excessive response and maintain the functions within the normal range. for example: if temperature and blood glucose level increases in the body, negative feedback loops control both the variables and maintain homeostasis.  

Hence, negative feedback loops used to control body homeostasis.