I think the reasoning is that Ash losing Kanto was memorable and, frankly, signature moment of the series even though it was a half-assed way to prevent it from ending too soon. You don't remember the anime where the hero wins (re: all of them). But where the hero loses, or dies in the process, the Ashita no Joes or Phantom Bloods, are talked about a generation later.
Mazinger Z is most famous example of this (aside from Pokemon). Ever Mazinger Z story ends with Mazinger Z destroyed, with Kouji yelling, screaming and crying as it crumbles about how "My grandpa's...My Mazinger Z... is invincible, it cannot die!". This scene is so strongly associated with Mazinger it doomed that mecha to job in every anime. Except the upcoming movie.If it happened for Mazinger, 40 year jobber, Ash is halfway up the stars of the Philadelphia Museum of Art
