Off hand no useful reasons come to mind. Can’t just be for the Purple Nurples. If you’ve never had the pleasure of being treated to one be thankful. That’s when a bully or best friend grabs your nipple and gives 3 to 5 hard twists. Excruciating! In the West I believe kids refer to it as a Titty Twister.
So back to the question of why God decided to keep the nipple feature in the male models. Gave it a google and found that the answer to be kinda lame. Apparently when we are in the early fetus stages we are gender-neutral. So just to be on the safe side, God (or whatever deity you worship) pops on a pair of nipples. That way if you go the female route all is good.
FYI…scientists say men do have the ability to lactate in extreme situations, so that’s a bonus. I guess.