The thing is... During the Diamond Pearl season (Yeah, I did some research), they were planning to have Ash win the league for good. However, after the Paul battle in the Sinnoh League, the writers changed their mind, and decided Ash should lose. That's why the character, Tobias (the character who defeated Ash, and we know absolutely nothing about him), felt really shoehorned into the show. That's because he was literally shoehorned into the show at the last minute just so Ash could lose to someone.
I did watch all episodes of the anime but after Battle Frontier I dropped it. Maybe because I was tired from seeing the same things. However, i kept a slight touch with it from time to time but that was it. In the Kalos League, i had my eyes on Alan and his Charizard. I was sure Ash was going to lose to him at some point. But within me, I thought that maybe, this time maybe, Ash stood a chance. Whether due to his deep connection with Greninja or him being finally to utilise his pokemon and his connection with them efficiently to finally defeat Alan as a payback for having lost to him two times already. Everyone thought it was Ash's time to shine! But instead the writers decided that he must lose again so as to reset again in the Alola region, and that as a reason for Ash to go there and explore the region with us while giving no respect to Ash a trainer and a character who really needs development. Many are tired after this and would rather see the Pokemon anime with a new protagonist eg. Red because what they saw in Pokemon Origins, which was more faithful to the games and their mechanics while having the concept of the anime, was more appealing to them and I can't disagree. In just four episodes we saw Red, mostly viewing him as a character, learning, maturing and doing things the writers wouldn't even think about Ash to accomplish.