It's not exactly "ashamed" I think, more like cautious. I mean, I've read multiple reports of people being beaten bloody on a candidate rally, so people would just prefer to stay out of trouble - even if they are proud of their choice, why they would risk talking about it publicly to random stranger? I mean, the pollster probably won't beat them up, but what if some crazy person overhears it and follows them and makes trouble? Nobody needs that. Sad, but such intolerance is part of the culture in US, many people just don't get "I disagree with you, but I respect your right to have your own opinion".
