Quoted By:
>According to an interview with Ken Sugimori, the character designer for the Pokémon franchise, the eponymous Pocket Monsters were given design flaws deliberately to amplify their overall look and win them fans.
>In the interview, Sugimori explains the importance of balance in creating the monsters, where overly serious monsters were given some element to take the edge off, or where characters considered too cute where given intentional imperfections.
>Sugimori explains that Luxray would look even better with a smaller head, and slightly more pointed eyes, but the decision not to make those changes was a deliberate ploy to stop him from being too perfect. With slightly off proportions, they figured, Luxray would make for a more memorable character.
So that explains why Shinx wears pants and evolutions being a "bigger" version.