I know, right! I couldn't possibly imagine what it would be like if people could attack really fast in URF!
Could you imagine what it would be like if Annie could stun people twice in one burst and always have her bear available to instakill any ADC?
It'd be a shame if Nidalee could chuck many long-range high-damage spears from a safe distance in order to harass the enemy team!
Oh, it sure would be terrible if Gragas, Maokai, Sejuani or Malphite were able to cc-lock people down for long periods of time and render them unable to attack!!
Ohhhh, wait. They do. Because they're allowed to use their attacks in super quick succession, while ADC's are not!
Playing an ADC that isn't something like Twitch or Draven is basically you asking to feed in URF because of this.