Because the writers recognized that too many story tropes would be entirely unreasonable in a post scarcity world and so wrote in a bunch of stuff that really makes no sense if you think about it too hard. Like why would someone pay for a drink at Quark's when every residence on DS9 has a replicator? Because the writers wanted DS9 to be a frontier town and a frontier town needs a saloon.
Also to be clear, everything I was saying in my above comments was primarily in relation to the Federation. I recognize there are parts of the galaxy where replicators are not common.