Why are surrogates all neat well-groomed supermodels?

I think it makes little sense. The human sense of aesthetics does not develop like that.

Now, everyone wants to look like a supermodel because in reality NO ONE looks like a super-model (and super models only look like that in glamour shots and under heavy makeup).

In a world where supermodel-perfection is the standard, physical human beauty would cease to exist. Beauty is the contrast between that which is appealing and that which is not. If everyone is equally perfect, where would the beauty be? Where is the incentive to be beautiful if the opposite sex is just as likely to brush you off because other people are just as beautiful?

It would be more likely that "natural" features would suddenly become a fad; people would purchase artificial blemishes and wrinkles to make their surrogates "more palpable". Those unconventional beauty trends and subcultures would flourish with custom-designed furry surrogates, chubby surrogates, perhaps even child-surrogates (perhaps disturbing, but victimless).

I understand that they were made "plastic" so that they would represent people losing their humanity, but society is not this homogenous. The movie really lacks plausibility, and tackles with interesting themes that it fails to address maturely.