Blue laws. Religious restrictions. And family rituals. None of those matter any more. No holiday remains "sacred," that is, off-limits for shopping in-person. Moreover, there are unique bargains to pick through on Black Thursay versus holding off until Black Friday.
In addition, more and more reasonable human beings are realizing that the opportunity to shop is a socially acceptable excuse to flee the family and other kinds of tribes who insist on holiday get-togethers. Even if we have to take them with us to the designer fruit market or the blowout sale in women's coats, that option trumps being held emotionally hostage in one house, apartment, or mobile home.
In the old days, when holidays were still considered sacred, dad went out for pack of cigarettes. Hours later he would return. "Every darn store was closed. I only found one open across the state line in Pennsylvania." Everyone knew. But he got away with it.
Shopping on Thanksgiving provides the same social license to exit the joys of togetherness. To ensure the total ability to enjoy each other, some families ban distractions such as television, videos, smartphones, and social networks such as Facebook. Those gatherings of loved ones are likely to produce the most Thanksgiving-Day shoppers.