Sorry I dragged the thread a bit off topic before. star*, this is a great question.
At first, I thought that intelligence is something that must be developed through work like reading and thinking. And that beauty doesn't require that work. But it doesn't take a lot of work to cultivate intelligence if you've got it - it comes naturally - and it does take work to look good and keep your looks as you age. So that can't be it.
Maybe it's jealousy? Everyone wants great looks, but only a few have it. Everyone wants to be smart (and likes to think they're smart), but it's the same, only a few have it. Maybe the difference is that with looks, everyone knows if they have it or not. But with intelligence, maybe people don't know if they haven't got it?
WAIT...another theory: it's how people *respond* to you. When someone's great looking, practically everyone responds to them positively. They have all kinds of things handed to them on a silver platter, in both personal and professional life. (There's a price to pay, too, but I have to assume no great looking person would say the costs outweight the benefits.) So here we have these people who, from the perspective of 90% of the population, have it oh-so-easy. Intelligence gets you none of this. Typically, the smarter you are, the *harder* life is! "Living is easy with eyes closed, misunderstanding all you see." So I think the difference is still jealousy, but based on how easy normal-looking people believe it is for beautiful people.
Arrggg...I'm scrapping that one too. How about this: without intelligence, we wouldn't have shit. No medicine, stories, music, airplanes, etc. There is a high value to intelligence. One person's intelligence, well-used, can benefit many. But beauty doesn't contribute anything to society. A great looking person is nice to look at, but doesn't do anything for us if we're not involved with them. And even if we are, the beauty only continues to have value if we like them for their inside as well. So when someone likes an intelligent person for their intelligence, we respect that because of its inherent value, but when someone like a beautiful person for their beauty, then we know that they're shallow, because we know that in a relationship it's the inside that matters, regardless.