Hip Flask, the rooftop bar at the new Marriott in Bethesda, was the first Marriott bar to really have some mocktails on the list. They are $14-15.. about the same price as most alcohol cocktails on their menu:
https://www.hipflaskrooftop.com/our-menus
Depending on the mocktail, their product cost can be lower (because liquor is expensive), unless they use lots of fresh fruits that are pricey. Then I assume they will offer food as food gets people to stay for at least 2 drinks usually.
Also, mocktail bars can offer to-go drinks while regular bars generally cannot (liquor license restriction).
So.. if you instead compare it to the economics of a coffee shop, it can make more sense financially.