Fun fact: The rise of Playboy magazine had a huge part in building the"girl-next-door" up as an erotic figure.
In essence, Playboy was all about Hugh Hefner's ideas on sex and displays of sexuality. Hefner associated modern (at the time) masculinity with sophistication, technology and a reclaiming of the sovereignity of the domestic space.
Subverting the post-WW2 standing of the house as the sanctuary of private middle class life, the magazine carried almost from the very start a recurrent theme of transparency and/or duality. This is most easily noticed in the articles aimed at the ideal city playboys Hefner envisioned as his readers. The famous rotating bed, music equipment and drink stations that popped out of the wall at the push of a button, and a focus on architecture featuring see-through glass prominently.
Following that line of presentation, the erotic pictures shown in playboy featured female models not in abrassive displays of themselves, but rather presented a certain voyeurism where it was as if the reader had found a hole in the wall and was able to peak into that woman's intimate moments.

That's the main aspect of it, anyways. There's more to be said about that but i've done enough writing already