This is kind of an obvious idea (in general) that for some reason wasn't obvious until very recently. Why would you show me two cars that are nearly the same ex

This is kind of an obvious idea (in general) that for some reason wasn't obvious until very recently. Why would you show me two cars that are nearly the same except that one is more expensive? Why shouldn't we just show the best flights (Hipmunk)? Why shouldn't we organize our Q&A site around the question and its actual answers (Stackoverflow)?