>>38776835Older style (arguably Gen 1 - 3) tried to design something more "detailed" to fit in a world and make them somewhat believable creatures, it's also why trainers design were super stylised back then. It's also no secret early Pokemon took a lot of inspiration from OG Dragonball.
Pokemon later on (Gen 5/6-7) started to get designed more based on merchandising, it's why you get the simplified shapes, solid colours, much more cutesy big headed designs, because plushies and toys look way better like that. It's why till this very day, Gen 1 and 2 Plushies and toys kind of look like shit compared to their original promotional art, yet the later pokemon look exactly like their merch.
Gen 4 though is very much an outlier as Pokemon went through it's Tetsuya Nomura JRPG zipper phase then.