re: Why do so many southern areas refer to themselves as americans on ancestry surveys?

Because southerners don't worry about the ancestry of who they marry. Thus, they aren't a majority of any particular ancestral group. What are you going to answer when you are 10% Irish, 10% Scottish, 10% German, 10% English, and part African and Indian to boot?

In the northeast especially, and other parts of the USA, Italians marry Italians, Jews marry Jews, and Poles marry Poles.