Replicators can't give you new territory, private property for your growing population, corp land to grow food at a lower cost than operating your replicator.
In spite of possessing replicator technology, the Cardassians were still removing materials from Bajor. There was a advantage to mining that material and a disadvantage to get a replicator to make the same material ... assuming it could.
That may be the problem--"in spite of possessing replicator technology". Instead of using this technology to its full potential, they still resort to preying on other planets.
The Cardassia are depicted doing this because they have to--they need to feed the people, they need resources to thrive.
Yet the Federation, specifically earth, is said to have eliminated poverty completely, and there are no needs or wants.
They don't even need a money system anymore, (according to them) because their technology, presumably the replicator- provides all their major needs. And even luxuries.
Even the land issue doesn't always make sense, in light of the technology that is known-- weather modifications nets should be able to allow crops to grow even in the most harshest environment.
Combined with replicators, it should make growing food really easy--assuming Cardassians mainly want to eat food grown out of the ground.
In order to have stories and plot lines, artificial scarcity had to be created, even if the technology contradicts the plots.
Isn't there something odd about Dukat saying that the Cardassians, while occupying Bajor, could have made it into a paradise, when around the same time another Cardassian Gul was telling Picard about how the wars on Cardassia caused planet wide hunger and poverty?
How can they turn Bajor into a paradise, if they have to go to war and prey on other planets just to 'feed the people'?