10k At the time Ash was signing up, we don't know if it's 100k or more now
I am not one of those who thinks that BF is Ash's best title so far, most of the brains on the frontier except Brandon would lose to Kukui and Gladio, plus Ash had to lose Brandon to win on the third try. In a Pokémon league, this doesn't happen, in a Pokémon league if you lose a battle, bye bye
This "only 10k" argument sounds like nitpicking, honestly. A lot of things in this anime don't make sense when you try to comprehensively analyze them. Just a few from SM :
why is tapu koko interested in ash of all people ?
why were the semi-finals and finals 2v2 and 3v3 respectively and not 6v6 ?
when exactly did misty and brock master mega evolution ?
why did guzzlord appear after the finals ( why not before that ) ?
why did melmetal evolve specifically before the finals ?
how the hell did torracat absorb that blast burn ?
why did nagandel appear right before his fight with kukui ?
why didn't pikashunium Z appear often, how does ash know to use it ?
why was ash in a dilemma after winning the alola league when he was pretty adamant about travelling when he won the orange league and the battle frontier?
and many more