I've been a boxing fan some time now and I always asked myself what is the purpose of wearing something that doesn't work. I mean boxers have had new advancements in gear like gloves, mouthpiece and even shoes. Why hasn't anybody thought of designing a cup that actually works?
It does work it just isn't foolproof. The cup protects against blows directly on it but not so much underneath it. And even directly a boxer punches so hard that the groin/genitals will still hurt despite all the padding. When a guy can punch you that hard believe me you will want the cup. Without it you may end up losing a testicle or something worse.
Muay thai fighters get knees and shin kicks to the groin and dont even wince. But some do wear steel boxes. I think boxers use it like rest time when the goin gets tough. See Judah vs Cotto. :deal
As Def already stated, they do work. They will stop a direct blow to the testicles, which could cause anything as severe as cancer. What hurts is the edges of thecup that dig into the bone next to ur family jewels. I don't know if you fight, but if you do and have had this happen to you, you know how it hurts. Pretty bad.
I think boxers should start using those, because the ones they use are just adding unnecessary weight and movement restriction.
The fact that so many boxers have produced children after their careers is living proof that the cups work. It may still hurt to get hit in the groin while wearing the cup, but if you were hit in the groin with the force of a professional boxer's punch without a cup, you probably wouldn't get up for the rest of the day, and if this happened to you repeatedly, it'd probably pretty well neuter you.
The reason low blows get so much attention was because years ago there was so much prejudice against Mexican fighters who threw body punches. Always remember that a low blow is below the belly button, not the belt. American fighters started wearing their belts very high to prevent body blows.