Good observation! Many of them calculate what they can get out of you. Moreover, many of them are racists. Having said this, however, I wouldn't count the honest ones out as they may lurk around for the reason that once they are seen with you they are doomed locally. Keep in mind that although materialistic girls are in big cities, gold diggers have been found in small towns as well. Anyhow, it's hard to blame the girls, since the Chinese moral code obligates the young generation to take care of the old one.