The difference could be linked to a number of factors: Those with higher incomes often have more reliable access to safely drinkable tap water. They tend to work in indoor environments, where air-conditioning may mean there is less need to stay hydrated. And they may be more aware of the potential health consequences of high sugar consumption.
When you are the 99% and are sweating your ass off I think people are thinking more of a cold drink to cool down more than, "oh man I better stay hydrated". And a lemonade tastes ace compared to another glass of water. And if you have enough money to have door to door AC it only makes more sense that like other food related things, if you have the means to have better your going to likely have better.