The Japanese and Chinese spin-off shows vaguely tie-in to the original series, but make changes to the world/characters to fit the demographic these new series are targeting.
In the first film they are forced together, and share a mutual dislike, bound together by circumstance. Their overarching character development though the franchise is about their friendship, and building of an ohana (together).
The title characters, particularly Stitch, have products a plenty, and are the focus of the franchise. In many ways, this allowed the supporting characters of Jumba and Pleakley to fly under the radar at a time when Disney would not have considered having an openly LGBTQ character. It would be eight years after the TV show finished airing that an out gay character would finally be shown on the Disney channel.