But first things first, let me clear up one thing - the whole thing about Ash's brain resetting with each new series is actually a myth. Ash's brain only reset once, and that was at the start of Best Wishes. The writers felt the need to do this for several reasons:
- The production team wanted to reboot the anime with a completely fresh start
- The writers completely rewrote Ash's character from scratch (as well as retconning his age back to 10)
- There was no direct transition from DP to BW, and this was the only time in Pokémon history where there wasn't a direct transition between two series
- Adding on to the above reason, they felt this was the perfect time to start fresh in order to minimize the confusion for younger audiences
- There was a certain trend at the time in which many classic anime (such as Yu-Gi-Oh, Digimon, and Pokémon) were doing "rehashes" of their own original series, as well as resetting a lot of formulas
Now I'm definitely not saying these are good reasons to reset his character, but I guess it actually makes sense in the long run. I'm really glad that XY is starting to add more depth to Ash's character, which is really surprising considering this is still "BW Ash" we're dealing with. (But hey, at least Ash didn't reset in XY, so that shows some consistency.)