have you ever taken a shot to the cup?
it doesn't need to be directly into your nuts for it to hurt your nuts. that's an unfortunate side effect of cups. you get hit square in the balls, they're not going to explode like fucking footballs, because there's a metal protector around them. you get hit hard enough at the edge of it, or get it grazed by a big uppercut, it will rattle your jewels to the point you'll want to vomit.
it may protect your nuts from permanent damage, but it makes the target bigger and more likely to hit. it's a trade off.
not saying it's you, but a lot of people on this board have never actually boxed and it really shows. getting hit / kicked anywhere on the cup fucking sucks, and is rightfully illegal.