We don't know how this pattern of alien Princesses being dressed in very skimpy clothing came about, but an early example of an author---who may have invested in "nubile" princesses as an easy way to increase sales---was Edgar Rice Burroughs.

In Tarzan and The Jewels of Opar, our boy Tarzan finally faces the princess of the--- well, the Opar gang--- and she wants to sacrifice him, because, you know, she's also a priestess.  They had no notion of separation of religion and state.  But he gazed at her like John Belushi, and she just couldn't do it. 

Then, over to Mars, with John Carter.  The princess Dejah Thoris.  Her princessly livery was designed to display all her charms, and once John laid eyes on her, he forgot everything else.  In the book, she goes about wearing only jewelry.  In the movie, they put clothing on her.  But the ideas of princesses, on the one hand, and revealing clothes on the other, are now inextricably tied together, so that even the Lords of Anime feel obliged to have their female royalty show a lot of skin. 

If the original creator of the princessly character did not clothe her in minimal togs, the artists at my favorite 'art' site repair the omission, and clothe Zelda, the demure princess of the Zelda game, as sluttily as possible.  Generally speaking, most of the skimpiest costumes on the site are worn by the princesses; to be a princess means to be half naked.  The Union of Princesses ought to go on strike over this travesty.  (Are they unionized?  I doubt it.)

Kay