It's well documented that fleas do prefer some people over others, though it's not fully understood why. A couple of likely explanations are particular scents that people give off attract them more, that some people simply react to the bites more, making them more noticeable, or a combination of those.

Anecdotally, when I lived with my parents and our cats caught fleas, we never thought of it as a big deal. We'd just see one occasionally. None of us ever got bitten. So years later, when my wife and I got a cat and it got fleas, I kept telling her it was no big deal, however she would be covered in bites. She would only have to stand in an infested area, and within a few seconds, you'd see them jumping up her legs. I would stand in the same area, and they wouldn't touch me. It was really strange.