This picture might be a good example. There are many people in a crowd and it doesn't matter we have difference tastes (E. g. some thinks blondes are attractive, other don't). Most of us have one thing in common and the thing is that we don't find everybody equal good looking. Some of us finds maybe a couple of them good looking, other doesn't find any of the people in the crowd physical appealing at all. Even though you find ten of them good looking, you still doesn't think all of them are and good looking people are still more rare than people who aren't.
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It's not all about looks though, I find proper grammar sexy too.
But the reason 'good looking people' are rare is that there wasn't enough incentive to weed out ugly people. Ugly people can still get into position of power, so they can mate with more females. This has been going on for thousands of years of human society. How beautiful a person is actually matters less when it comes to reproduction, having more money means you are more likely to have healthy offspring in today's society, and having more money has little to do with looks. Also, you can be a manipulative person or a rapist without looking good. Also, people often settle down with others who aren't particularly good looking because they have other redeeming traits. Some of my gfs were like that, even though I am fairly handsome, I've dated girls way bellow my league because they were cute enough for me, they were smart, funny, or had some other charm.
In ye olde times, rich people had harems, so leaving a ton of offspring depended on how wealthy you are. Also wives were often bought, as well. Nowadays it's way more about personality and being capable of persuading somebody to leave offspring with you.
TL;DR: Looking good doesn't drastically improve your chances of leaving offspring behind, it never did, but the reasons have somewhat changed throughout centuries.