I doubt if desperation has much to do with it, any more than, say, the difference between a pedicurist with a smart salon in the town and the local lady who comes and prunes my toe nails (which I can no longer reach). Car meets involve no overheads for the girl (no rent, furnishings to purchase, or cleaning up between customers) and are far less complicated timewise between a series of appointments, so a girl who does it "on the hoof" probably has far less hassle than one who works from a fixed address.