It's the same reason Hermoine picks Ron. The same reason something happens to turn everyone against Harry even though he should be worshiped as a God. Same reason Bella Swan is designed to be average. It's so the majority of people can place themselves in their shoes and relate. In actuality, Harry would bang out every girl in school and his ego would become more massive with each one.
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Realo won gold at the Sex Olympics with a BROKEN FRIGGIN NECK.-Voltch