Not because it's the biggest shopping day of the year.
(If one is to implement holiday-traffic-avoidance measures in the SF Bay Area, one must, starting on November 1, cut out all travel between 3pm and 8pm and avoid all large stores or agglomerations of stores - anything that has a parking lot. Merely skipping driving to stores on "Black Friday" isn't going to make a difference to one's traffic-related stress level.)
Not as a boycott. A boycott is actually never buying something until the reason for the boycott goes away. It's not refraining from buying something for one day.
Not as a way of feeling superior to anyone.
Just as a way of thinking about my buying choices, and the buying habits of my culture in general, and the fact that I'm lucky and privileged enough to have enough food in the house and work that I can do at home so I didn't have to go out on Friday.