Nothing was ever interest-free. It was just built into the overall price. You were incentivized to put it on your credit card, but the 30% inflation was still tacked on. Whether you paid it in 12 installments, three or one, everyone was paying the interest. I am unaware of how much the stores themselves made off of this, but it must be so important they are essentially unable to lower their prices by more than 5-10 percent. In other words, they got used to that added cash flow, and now (especially now) can't do without it.
The government's aim to bring down inflation amid a recession and global economic stagnation is pure stupidity to me. If I were in the Central Bank, I'd be far less worried about inflation and more worried about keeping the exchange rate competitive. Instead, they pursue policies that cut government spending while 1) hunting down Argentine money abroad so they can stop printing money and 2) raising interest rates sky high to encourage excess pesos to be deposited in fixed term accounts; all of it together depresses the exchange rate, hurts Argentine competitivity, encourages imports and disincentivizes investment into the real economy.
If you're a local or foreign investor, why invest your money into productivity when you can just put it in a LEBAC and make ~20% annually, withdraw, and buy dollars at the same or a lower rate?
As I know they are not stupid, the only conclusion that I come to is that they must represent different interests, certainly not the interests of those who rely on the real economy to survive.