The majority of bicycle thieves in a university city are men. And not just men, "real men", you know, the type that wresles bears, eats nails for breakfast and drinks hot lava out of a mug with hair on it. (Or at least they think/act they are. Actually most of them are just student guys who act though). The type of guys that wouldn't want to be caught dead riding a pink bicycle, because that's for gays and girls.
It's using they're own prejudices against them.
Also, if you steal a bike, and you have a choice, steal one that isn't noticable. Especially if it's for use in the same general area as where you stole it (which is mostly the case in uni cities). My bike got stolen two semesters ago, and if I would see it somewhere, I would take it back. Sadly, it's a rather generic bike, and I would really have to look in detail to see it's mine because there are a lot of those out here. But if it's were noticable bike...
"It is better to shit yourself, than to die of constipation." - Some picture on reddit