I think it is about "passing" so to speak. No one wants to look "ethnic." (except me apparently
I grew up in Albany, NY. A city that was mostly Italian, Irish, Afro-Am and Jewish. When I was growing up I pretty much looked like everyone else and most people who didn't know me assumed I was a little Catholic Italian girl. (like everyone else)
When I went to college in Wisconsin, the ethnic makeup was very different, suddenly I was shorter, darker and people who didn't know me often guessed that I was Jewish. (except two times when I was asked if I was Puerto Rican and Persian by a Puerto Rican and a Persian respectively.) I thought this was interesting, in Albany I blended in no problem, but in Wisconsin I stuck out. Many of the other Jewish women I met (who were out of state students from NYC burbs and Chicago) dyed and straightened their hair to the point of damage.
I think that Jews have definite issues about "looking Jewish." Don't get me started on the term....
BTW check out the thread on the General Board about the Genetics of Hair Texture. There was an offshoot about Jews on there. (my fault)