It's also an opportunity to drop stock you don't want before the end of Q4.

My impression (about the retail version, say 15-20 years ago) was that it was companies offloading stock they wanted off their books at something of a discount ahead of the holiday season, since it let the companies close out their books for the year and customers get a little bit more for the holidays. It was a win-win in a lot of ways.

Then the disgusting marketing/accounting shenanigans took hold and made it shitty, particularly the online version. It's still possible to find genuine deals, mostly because retailers do still have stock they want to offload.