This is admittedly more speculation than fact, but I think that since the beginning of the financial crisis/recession, Black Friday and its sales have become more important because
1) Retailers will do literally anything to squeeze more money out of consumers before the end of the fiscal year, in order to look good for investors and regulators.
and
2) Those same consumers who wait special deals such as Black Friday to buy things are probably buying on credit and/or have drawn down much of their savings, making them less able to "time" the market for the optimal time for big-ticket purchases. In other words, these people probably didn't have much money to spend earlier in the year, due to unemployment or some other factor, and now feel that they have to buy stuff for the holidays that they had previously put off getting.
But maybe I'm wrong.