Because New Coke worked out so well...
Actually it did in the long run. Sure New Coke itself bombed, but when they brought back regular Coke sales were much higher than they had been for years. It reversed a slide that had been ongoing for nearly a decade. Which is actually probably a big part of the reason for these temporary changes. Like IHOP to IHOB and this thing. Generates a lot of publicity, and renews energy for your “old” thing which you fully intend to bring back anyway.