Uhhh no? Soda is literally the cheapest item a restaurant or bar sells. Do you think they have a secret RC cola line from the soda machines so they can save .02 cents per already marked up by 50% rum/whiskey and coke?
Are you getting that mixed up? Because sketchy bars will absolutely switch the liqour you asked for for well stuff if they think you won't notice.
Maybe it's regional. I've worked at a number of independent bars and taverns in and around the Midwest and only one had Coca-Cola mix. The others all had "cola" by whatever distributor the owner sided with.
The one place that has real Coke had a bright red soda gun that literally said Coke on it, the others were just black and the button said Cola.
I don't miss changing out those nasty, sticky boxes.
I think you may be thinking bigger chains wouldn't order off brands, like Chili's.
I have no doubt it's regional as hell. In my experience, though, no one is going to skimp on soda. Generally, it'll be the first thing I'd give for free if it seemed reasonable.