Maybe because they feel that they clicked with you.
This is a strange business.
I guess one reason would be that some of us hold out a bit of hope that maybe, just maybe, a provider saw something in us other than the money in our pockets.
On the provider end, most try to be as friendly and sexy as possible for there customers whether they 'feel' anything or not. On the flip side, us mongers only see this friendly and sexy side. We dont know, or ignore the fact, that everyone gets the same treatment. I think it's pretty easy to mis-read the signals from the monger end, if your not wise to the business.
If a provider digs you NP4P, she will let you know. Otherwise, just enjoy the fantasy.