Not only because of Ash x Serena being *the* closest we ever truly got, or possibly will get, for an actual pairing, but also because...well...it's how the series has always been in "resetting" Ash to almost zero every season. They'll tease moments throughout the series until the end with nothing actually becoming of it.
To have Ash in any sort of actual relationship, winning leagues, and so on would mean having to have him actually grow and develop as a person and Trainer and staying that way, which would mean that they would have to have Ash start actually aging and growing up, which would mean that Ash would eventually no longer be the relatable "kid" for Pokemon's demographic (children up to ten years old), and thus they would eventually have to find a new main character with a new Pokemon mascot to fill that slot which would more than likely not go over well with much of a fanbase.
Yeah I know, that's why I have NO expectations in that regard (shipping and winning leagues)
Edited by Phantom_999, 15 March 2017 - 10:41 PM.