Christmas is often the sales that put store in the positive cash flow for the year. (Which is why black Friday is called black Friday. They are no longer in the red.) They will milk those sales for as long as they can.
That's a myth about Black Friday. It's name comes from the Army/Navy football game the day after Thanksgiving when people would rush into Philly and the whole city would be in chaos. The police gave it that name. The sale idea came because lots of retailers there would have weekend sales since there was so much out of town traffic.
I notice the "black Friday" sales seem to be advertised well after the day. Funny how that is. All those fools that kill themselves to get out that one day can easily wait if they paid attention to the ads.
Most stores get rid of their Christmas stuff with sales. They don't have room to store all that stuff, with new stuff coming in. Stores also start filling their shelves with the next season's items before the season gets here. People buy a few things at a time to get ready for the next season, as Spring. Planting season in central Texas started mid February, so people start shopping in January---right after Christmas.