User blog comment:The ASL Pirates/Will Someone other than Luffy Fight the Strongest Opponent?/@comment-96.42.191.111-20150620235835

One idea is that some how Luffy is unable to participate in the fight due to sea water or a seastone item, such as being in handcuffs or the main opponent wields a seastone sword.

I could see others getting big fights, like Ussop in Elbaf or Sanji having been trapped with a main opponent that is a woman(likely ugly).