I dont think its just white girls, but american girls in general.
Our culture promotes popularity, personal advancement, and selfishness particularly in women.
I find that european women seem to be less selfish and are genuine in a relationship. They want the experinence of dating to be enjoyed mutually. American girls just test you over and over and over and over again to see if you her "prince charming". The problem is that a lot of women have a delushional idea of what "prince charming" is.
European girls, ime dont seem to be caught up in all that bullshit as much and can just enjoy each others company in a less formal and more casual way.
American girls are more caught up in stupid formalities, the mean shit if you got married. Just my 2 cents, or euros.