One reason could be that the fanfic has a strange or unappealing plot. For example, if it makes Ash do something completely out of his character, like being mean to Misty for no good reason.
Maybe the fanfic contains inaccuracies about the Pokémon world that Ash is a part of. If it misrepresents the relationship between him and Misty in a way that he doesn't like, he would reject it. Also, if the fanfic has a very dark or inappropriate tone that doesn't fit with Ash's positive and adventurous image, he would not be on board with it.
The possible reasons are many. Firstly, the fanfic might not be in line with the official Pokémon storyline that Ash is accustomed to. His character development and relationship with Misty are important aspects in the official story. If the fanfic distorts these elements, he would reject it. Secondly, the writing style of the fanfic could be off - putting. If it's too convoluted or hard to understand, Ash (as a character in this context) would not be interested. Thirdly, if the fanfic focuses too much on a romantic aspect between Ash and Misty in a way that Ash doesn't feel comfortable with, given his more friendship - and - adventure - oriented personality in the official story, he would reject it.
Chapter 164, "The World in the Mirror, Immortal", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. The setup is Below the bamboo building, the crowd was bustling, with faint noises..., but the pressure keeps building through The moment Yuwen Hu finished speaking, the scene froze..
Chapter 200, "Xu An, Ten Thousand Urgent, Presenting Treasure (Part 2)", is the clearest early answer because Great Xia gets a payoff that changes the stakes. It opens with Any matter related to the hunting team is critically important. and closes on They are now located at the edge of the North Slope, almost stepping....
Chapter 185, "New Home, Land, Arrow Bamboo Forest", is the clearest early answer because the buildup finally cashes out in a real clash. A useful checkpoint is the way the scene starts with And the grand golden chair on the high platform added a touch of... and follows through with Therefore, the allocation method will not change!.
Chapter 204, "Homecoming, Unease, and Birds", is the clearest early answer because it turns Xiang Liang's situation into a concrete plot event. It opens with At most, only about a thousand Earth-digging Realm cultivators. and closes on Not just him, but many people beside him, too, widened their eyes,....
Chapter 196, "Sword Puppet, the First Intermediate Squad", is the clearest early answer because it turns Thunder Kui's situation into a concrete plot event. A useful checkpoint is the way the scene starts with First Year of Great Xia, May 20th Redwood Ridge, three kilometers... and follows through with The light golden exterior of the Thunder Kui provides strong defense;....
Chapter 193, "The Army, The Beast Tide, Little Snow Mane", is the clearest early answer because it turns Xia Hong's situation into a concrete plot event. The chapter turns that into something concrete by moving from Population really is the cornerstone!" In the back of the main hall,... to As for the army matter, that's even more wishful thinking..." Xia....
Chapter 232, "Saving Lives, Putting on an Act, Xia City in Uproar [8,000-Word Chapter, More to Come]", is the clearest early answer because it pushes Peng Bo into a new phase or setting. The setup is Five against two, a fierce battle reignited., but the pressure keeps building through Brother, could you hand over the three children to me first?"....
Chapter 179, "Tigers Fall, Witnessing and Floral Heart [Happy New Year]", is the clearest early answer because it turns Xia Chuan's situation into a concrete plot event. The chapter turns that into something concrete by moving from These beasts, they have completely lost people's hearts. to Seated on the chair, Xia Chuan turned his head to look at Liu Erhu....
Chapter 250, "Rescue, Intimidation, and Surprise (Part 2)", is the clearest early answer because it turns Long Mountain's situation into a concrete plot event. The chapter gives readers a real answer by opening on Those people in light gold armor have been using solidified fire oil... and ending on That thing can actually eliminate dew, it's amazing!" Among the three....
Chapter 243, "Hanqiong's Great Battle, Realization After the Fact (Part 2)", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from Xia Hong surveyed the houses inside Hanqiong Station, marveling at... to There's an enemy attack, hide quickly." "It's real, someone's....