The journey IS the destination, though. If they wanted to focus on the journey, they shouldn't have even BOTHERED giving Ash a goal in the first place. In fact, just have him say he doesn't care about winning or even having a goal, just having an adventure, like Sonic does, or even that old adage about how it doesn't matter if you win or lose, but just getting out there to play the game. Instead, Ash has an explicitly stated goal, and the entire point of even HAVING a goal is to achieve it. And in order to achieve it, one needs to actually REACH the destination.
If the journey was truly the true message of the anime, they should NEVER have given Ash a goal in the first place. I know if I were writing the series and that was the intended message of the anime, I'd make SURE Ash and the others NEVER give a goal other than 'hey, this sounds like fun' specifically to REINFORCE how it was never about the destination (no goal = no destination). Heck, even Dragon Ball doesn't have Goku having an explicit goal of becoming the absolute greatest Martial Arts Master, just the best he can be. Heck, considering that he constantly resets at the end of each region and doesn't seem to retain much of what he learned, we can't even say it follows through the intended theme anyways (if it did, Ash would have actually RETAINED what he had learned and not have his Pikachu especially undergo level resets), since even under the argument that it was the journey that matters, not the destination, he needs to actually RETAIN that knowledge he gained on the journey for the journey to truly matter.
Even ignoring all of that, however, it's not like if Ash actually beats Alain, he's finished. Remember, DP revealed that even if he won the Sinnoh League, he'd still need to challenge the Elite 4 and Champion before he can truly become Champion. They could have had him beat Alain, yet lose against an Elite 4 member, so that he technically beats a league, yet still has work to do before Ash truly manages to succeed in his goal.
Instead, we most likely have to wait until Generation VIII before he even HAS a chance to accomplish his goal.