>>55408116Combo of a bunch of things.
XY basically depicted Ash at his most competent and mature, which is something people had been asking for for years - he was too experienced to still be making dumb mistakes like in the previous series.
The series itself also had a much more shonen-esque tone with a lot more focus being placed on rivalries, battles, power ups and things like that - it was still obviously for kids, but you wouldn't have as many episodes that were just the characters playing with Pokemon until Team Rocket arrives and stuff which were so common in the first four series (you'd still get a few though obviously)
All this stuff lead people to think Ash actually had a shot at winning the League, which of course he proceeded to not do. That on its own got a lot of people pissed.
Ash was also pretty useless in the last Team Flare arc where Alain got a much bigger focus, it stung since he's the one that beat Ash in the League.
Then to rub even more salt on the wound the Sun and Moon anime was completely changing the tone and style of the show to an SoL comedy about Ash going to school to learn the basics of Pokemon battling, completely undoing all the goodwill they'd built up for his character with the XY series.
I actually do enjoy the SM anime, but it is a big departure from what XY was doing so it's no surprise that fans of that series wouldn't like it.
