I was a collegiate football player (FCS though so nothing crazy) and then played rugby in grad school and beyond. You'll still see some linemen wearing cups. I was a tight end and blocking can put your nads at risk with another guy trying to out-position you. Most skilled positions don't. Cups can slow you down a bit bc no matter how 'lightweight' they are marketed, they still cause a bit more friction down there, and can easily move out of place and that can get really uncomfortable, really quickly. They can also jostle from the force in non-groin hits and cause pain and bruising too. But it's really up to the player. I caught a low ball in my junk during a game once and wore a cup for the next couple of games after that. Even though it wasn't super comfortable.
