I will never understand why they refuse to let him win. I don't watch the anime anymore (Him always losing at the Pokemon League is a big reason why), but its not like the show would suddenly have to end.
Yes his reported dream is to win the Pokemon League Championship, but just because he beats one Region doesn't mean he wouldn't want to go to the next one and win as well. It would honestly be an even more interesting storyline since that could let them explore him becoming semi-famous and how that would work with him starting over in the new region.
Especially when the anime's whole shtick is "You want to be Ash and use Pokemon too!" and yet he loses literally every timer he goes to the Pokemon League. Its nonsensical.