>>37630000He isn't because he's not allowed to.
Every Pokemon series ends with Ash boxing or releasing his Pokemon and beginning a new adventure in another region. This is so that each series can feel like its own thing without the newest kids in the target demographic don't feel like they have to go back hundreds of episodes to get the full story.
Including a romantic partner for Ash in a series would mean one of two things: either their relationship would have to end by the series finale, or they'd have to bring her back in the next series and have it established as the norm. That's why the closest they've ever gotten was Serena kissing Ash before they parted ways for good.
In the same way that Ash is not allowed to grow up or have an established team across regions, he's not allowed to have a romantic partner. It's a corporate formula, and people on here debating about who he'll end up with are just setting themselves up for disappointment.
Digimon never had this problem because each series was centralized around a new group of characters. There was nothing stopping the characters from having their own arcs and growing up.
