Maybe it's simply not standard Cardassian procedure to self-destruct if forced to abandon a station like the Nor-class. We know that it is for Starfleet vessels and stations, if there's a chance of military equipment and/or secrets getting into enemy hands. But the Federation is plentiful, while Cardassia has always been a resource-poor culture - that's the whole reason they invaded Bajor.
So maybe, as the others have suggested, they deliberately left the stations largely intact with the hope that one day they would be able to return to collect that hardware, rather than wasting the resources on destroying it and having to build another. And the psycho soldiers were their booby trap security system in the meantime. It's their own way of stopping military secrets falling into enemy hands - anyone who tried wouldn't survive the attempt.