No one said the replicator can perfectly create the most delightful and exquisite flavors and aromas associated with the real thing. Also the bar is like a real bar in a way, you’re not paying for just the food/drink but also the atmosphere.
Also also it’s a Bajoran station, so maybe Quark has to pay an energy bill even for using the drinks replicator.
Also also also Quark makes the point that he had programmed the drinks replicator to be even better than a regular one, so you’re also paying for that.