People just don't understand evolution, that's all.
Attractiveness isn't some magical universal quality. What people find attractive is determined by evolution. We find people attractive in ways that our ancestors found them attractive. People who were wired this way survived and prospered. People who found other things attractive died out.
The only trouble is that these ancient hardwired ideals of attractiveness don't necessarily apply well in the modern world. A lot of it is tied up in health. To a very high degree, somebody who's attractive is also healthy. That pretty face or those curvy boobs held the evidence of fewer childhood diseases, of less likely or less dangerous genetic disabilities, of good nutrition, and of good ability to survive. It makes good sense to mate with somebody like that! However in the modern world it has become very easy to avoid childhood diseases and obtain good nutrition, so attractiveness and fitness have somewhat separated.
Still, even though it may not match up with what's best for us as well as it once did, it surely is far from being purely superficial.