So, tell me, if this anime exists to sell products, then...
•Why isn't the star of the games the star of the show?
•Why write a "bad-ending" contrary to the values drilled into people by the series?
•Why are the villains so dumbed down from the games?
Face it; some bits of this anime can't even be justified from even the most amoral, capitalistic perspective. The plots of the video games aren't good themselves, and unlike some here, I'm willing to blame them for many of the anime's problems, but still the anime just diverges from them in ways that at best make no difference in their goal of promoting them.
Some have asked why they should change when the current formula is working just fine for them. The answer is that it's not; the anime is just being floated by brand association; not it's own (lack of) merit.
Saying the whole thing is marketed to ten-year-olds is actually pretty reductive as a business mindset, because who here can honestly say their first Pokemon game was also their last? If you're like me, and everyone I ever asked, you beat a region's league, became the champion, and still bought another game afterward to start fresh in a new region with new monsters. You best believe they value the income of return customers. If Ash is supposed to be a stand-in for us, the players, at whatever age, why not realize he can win a league with a powerful team, and still start fresh next time?
Let's be real, though: I want Ash to win, I want him to age, and I want him to find some sort of more permanent happiness like finally meeting his father, hooking up with one of the girls, etc, but above all else, I just want him gone. I've constantly ground my axe that Ash really contributes nothing of value by always being the star of the Pokemon anime--he's always less-relatable to people in the long run, he's not the actual male protagonist in the games, and constantly giving attention to his glory-hounding quest lessens the ability of the female protagonists to come into their own as characters. Perhaps worst of all, though, is that Ash constantly moving on to new regions has undermined one of the few things that was ever remotely wholesome about this mostly-cynical cash-Miltank; the sense of camaraderie. This is why, although as stated above, it's entirely possible for Ash to win a league and still move on, "moving on" at all makes it seem like he cares more about his own rep than he does about his friends. Really, can any amount of "it's for kids" justify that? I think if anything, exposing them to such a sociopathic outlook is all the more rancid because they don't know they're being conditioned. All this could be solved completely if they just gave us a (the) new protagonist with every region.
So far as I can recall, the only sendible rationale I've heard for keeping Ash around is his association with Pikachu. Because that's his main, and not necessarily anyone else's, by having Ash in the anime they can keep their arbitrary mascot mon in as well. Admittedly valid reasoning, but here's a possible counter: Pikachu himself is so widely marketed these days that he probably doesn't need Ash. When this series first debuted, nothing in the games themselves presented Pikachu as the star, but since then, he's the star of almost every spin-off game. That, plus some tie-ins in the main series--Cosplay Pikachu, for example--is enough to make him popular.