I mean dunkin serves 396mg of caffeine in their large iced coffees. Just eyeballing it, their large iced beverages seem to be 30oz as well. I don’t think that the serving sizes are much of an issue when compared to other beverages with similar caffeine content at other restaurants and cafes.
We’re talking about people who have absurd amounts of money. I know a rich guy and he doesn’t even blink at spending $10k+ on some things. It’s just inconsequential.