For me, it's Power over Cuteness, too. I've only stopped one evolution. Eevee. My Eevee started to evolve into an Espeon, and I prevented it. Kept preventing it (both Espeon and Umbreon) until I just gave him an everstone. I love Eevee. It's not a cute thing, I've just always loved the Pokemon. I eventually evolved him into a Jolteon, though.
Other than that, only unevolved ones I've had were the ones that evolve through trade. And that was because I never had access to trading. Until I got a wire to do so for Christmas one year (from Dollar Tree, too. lol But it worked for like five years, so I'm not complaining) and even then, I couldn't find anyone to trade my Graveler or Kadabra with... I spent all those years wanting a Golem and an Alakazam... and now that I have them on Platinum, I don't even like them. So, I'll probably have an unevolved Kadabra next reset.