She doesn't want to seem easy, dirty, slutty, insert your adjective here, and by making this more of a 'romance' of sorts, she hopes to avoid this.
Its also the wrong way to go about finding someone. Sure maybe you will find that proper couple, who wants to do that same, and is not willing for that sexual tension to get in the way, but you might get hit by a train as well.
You will be meeting a people, with the intent of having sex with them, eventually.
This is hard enough in vanilla dating and you have the whole 'relationship' part of it as well.
Again I'm not saying it can't happen that way, only you are most likely really setting yourself up for disappointment.