>>57126763Which as we've come to find out, is because they genuinely don't know how to make more Eeveelutions without risking the controversy of a fan stepping up and calling them out for plagiarism. They've tried a fuckload of design concepts for a Flying Eeveelution in Alola, but every single one of them aligned too closely with a pre-existing fan design that they scrapped it entirely.
This is also likely why there was a prominent Eevee in Power of Us, an anthology movie centered around a SKY Festival. It was going to evolve as part of its trainer's character arc, but they scrapped that aspect early into production when they got word the Flying Eevee wasn't happening, and the same likely happened to Chloe's Eevee, when her literal entire character arc was "What do I want to do/be?" and how Eevee reflected that.