I always thought the practice to where finance charges are accumulated and charged from the date of purchase if not paid before a promotional rate comes due was a Synchrony thing. I just got a notice from Citi/Wayfair that they have the same setup. That sucks! I thought better of Citi. This doesn't really affect me as I don't use the card and keep the card open for the 20k in revolving line, but this is insane. I feel bad for anyone who retroactively gets hit with interest at a rate > 30%. This sounds cruel.
One little word makes all the difference... "Deferred".
I have Citi for Best Buy and Home Depot. Both offer some options for 6,12,18 or 24 Months of zero interest as long as it is PIF by the end. I bought an OLED last Christmas for 3k on a 24-month deferred interest. In all fairness, I will say that Citi does do a good job (in my opinion) in keeping you up to date on how long you have left and how much interest will be added on IF it is not paid in full by the due date.
Below is a snip from my BB acct.. As you can see it's pretty transparent - no guessing and no way you would be 'surprised' at the end (unless you never looked.) So I have to give them that. It can be a useful tool to make a big purchase. Like lay-away using their money for 24 months. LOL
Indeed, deferred interest isn't quite the same as *NO* interest. Although of course companies will often use these two words interchangeably.
But to your point, it's not exclusive to Citi. All banks do it. Comenity, Synchrony, WF with their furniture store cards, other smaller banks backing furniture/rent to own stores...the list goes on.
Deferred interest has been around for a LONG time with many creditors. My parents bought a bunch of new furniture in 1985 and got hit with back interest when they didn't pay it off in time - that was one of the first lessons they taught me about credit! 