Display Moreok let me try answer the actual question:
visuals in kpop is not different to pretty people in real life or other pretty people in different entertainment circles around the world.
there's certain statistics that show pretty people get better treatment in life.
11 scientific reasons why attractive people are more successful in life | Business Insider
So why shouldn't it be any different in kpop, in a lot of groups the visual is the first thing that catches your eye even before the first note is sung or instrument played.
In real life (ceteris paribus) we would prefer a pretty partner to a less pretty one
Yes, but in Kpop all of the idols are pretty. Your comparison is between beautiful and average/ugly looking people.