This is due to the nerve structure in the male organism. Initially, the testicles are formed in the abdomen and descend to their final lower position. For this reason, most of the nerve endings go to the abdomen.
However, the sensation and tolerance to pain may be different in each male. The brain will send the pain signal and it will travel along the nerves. Therefore, the pain will be felt throughout the body, but especially in the abdomen.
Suggested for you: Testicular Trauma: Cause for Male Infertility?.