One wonders... There had been a goddamned war
in the region until 2362 or so, and the Federation had not paid much attention. Why should a mere "incident" change things? Especially when the UFP apparently had deliberately chosen to ignore this region, and to give the Cardassians a lot of rope to hang themselves with.
And the "secret shipments exposed" thing still concluded in Picard demonstrating that the shipments could continue with impunity.
One might compare this to the late 1930s where the Nazis were caught red-handed on many an issue, and Mussolini gave them a serious slap in the wrists diplomatically. The suspicious paramilitary activities still continued, the distribution of supply assets for an extended naval raiding campaign (a close analogy to the Cardassian effort) proceeded at full steam, and standing policies regarding Germany were considered to remain standing, the recent victory over that nation still fresh in mind (again a decent analogy to the Cardassian situation). And the surrounding nations were not weak by any military standard - discounting the immediate buffers like Denmark, Poland and Romania, each and every one of them individually outmatched Germany in everything but audacity - so a degree of complacency was certainly warranted; all the more so in the case of the UFP.
Given how much the Cardassian Union was indicated to be an underdog in "The Wounded", an invasion timetable of three years of preparation cannot lightly be declared a "delay". For all we know, it was a move ahead of the original schedule.