Purrloin steals because, in the Pokémon world, it’s literally described as a mischievous cat Pokémon that takes things for fun and for the reaction it gets from people.

In‑universe reason

  • Purrloin is a mischievous Dark‑type Pokémon that “likes to steal from people.”
  • Pokédex entries explain that it steals just to amuse itself with its victims’ frustration and to see the looks on their faces.
  • It puts on a cute act as a ruse; when people let their guard down, it swipes their valuables and may leave them with scratches and bruised pride.

Personality and theme

  • Purrloin is themed after a cat burglar: a sly, charming thief who uses cuteness and deception instead of brute force.
  • As a Dark‑type, its stealing fits the type’s general theme of trickery, pranks, and underhanded tactics rather than straightforward battling.
  • Despite the theft, victims “can’t help but forgive them,” which reinforces its role as a lovable troublemaker rather than a truly evil Pokémon.

Name and design hints

  • Its English name comes from “purr” (cat sound) and “purloin,” which means “to steal,” baking the stealing behavior into its identity.
  • Its behavior, rivalry with Nickit, and sneaky animations across games all support the idea that stealing is simply part of what a Purrloin is.

TL;DR: Purrloin steals because it’s designed as a cute little cat burglar Pokémon that enjoys pranking people, using its charm and tricks to snatch items purely for fun and reactions.

Information gathered from public forums or data available on the internet and portrayed here.