you want it explained? it did not used to be like this. it happened after the sexual revolution in 60's 70's and when women gained more independance during the 20th century.
now women feel free to do what ever they want, and they want to copy what hollywood does, which is look sexy, and they like to be the prettiest girl so they compete.
not all girls are like this, but a hell of a lot
its not going to change so you will have to get used to it