Because if everyone was would they still be known as good looks?
Everyone would just be average or normal and we would still seek someone that's different or more attractive than the rest... If everyone was attractive attractive would no longer be attractive it would be common or ugly.
Good looks aren't always a blessing. Most people, if they're not super attractive on the outside, they have really good personalities because they're not getting positive attention a lot and when they do, they appreciate it. Like have you noticed in movies... The popular guy is really attractive, so he's used to getting the affections from people and he doesn't really give a shit. Or there are the people that are attractive but don't know it. I think these are the best kind.
In one sense, we base who has "good looks" or not by who looks better compared to others. What is attractive or not is relative. So the only way everyone could be born with good looks is if everyone looked exactly the same, and that isn't realistic. It's not fair, but in life, very few things are actually fair.
It is kind of the same concept of saying "If everyone was special, no one would be special anymore"
Because of the gaussian distribution. Most people are going to be average. Why would you expect most people to ahve good looks? If everyone had good looks then we'd still all be average, which makes your entire premise stupid.