I would assume it is formulated to compliment the sweetener. Cane sugar remains a cheaper option in Mexico, a nation without quite the same King Corn subsidies as the US domestic market. Also cane sugar stays in reach because gringos will pay like 2 bucks a bottle for the stuff!. Market driven for the big players is my point.
Also, HFCS came in around a time that the US was having problems with sugar plantations on a certain island nation just off the coast of Florida.
It’s only when corn prices spiked here the other year that cane sugar soda from large producers became a thing again in the US. Currently the pricing is about even, so I expect pepsi to keep making the throwbacks. I don’t expect HFCS to go away without a Jenny McCarthy… why couldn’t she have focused on something actually unhealthy!!!