Mostly because other's doesn't view just a single pretty girl's profile, they go through multiple and by the rule of "if you do something what other's do, you are bound to do what they have done but you didn't yet"
In technical terms, this is called collaborative filtering. This is also some sort of positive feedback loop -- LinkedIn shows pretty girls -> people click on pretty girls -> algorithms learns to show pretty girls, and shows them even more -> ... and so on.
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