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Why do people seem to forget that this is a children's game aimed, developed, and marketed towards children?
Children, usually, don't have an idea of what's fair, rare, or worthwhile.
All they see is "I don't like this pokemon" I'm going to put it up for "the one I like/want".
The ones you see are the ones that don't get traded because the "good" deals are snatched up within minutes.