That happens to some extent but many jurisdictions have laws regulating the practice of increasing prices just to cut them as an advertised discount. For national retailers who do nationwide campaigns, the hassle of structuring deals in a way that is compliant with all state and local laws would be significant.

Nope, there are some pretty sweat deals when you compare prices before and after the period.

It might depend on the industry though.

There are real deals too, but often with a catch "last year's flagship model for 50% off", or "buy x and get a $100 gift card to spend with us next year", etc. And for brick and mortar stores, even a decent discount may still be more than shopping online, especially considering out of state online stores don't charge sales tax.

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.