I think it'd be valuable to define the term "nation" here. The modern concept of a Nation (centralized government, national directives, support of overarching, homogenous* organizations designed to keep the system running smoothly, deliberate collective support of any other part of the nation should it fall under some disaster) doesn't seem to fit many of the pirate factions.
Some of them, at least, seem to me to be far closer to feudal "patchwork-princedom" nations - i.e., there's a local heirarchy of people culminating in some kind of bigwig, who in turn pays tribute to and may follow vague orders from a higher agency which provides some form of limited support, often in the form of reinforcements in the event someone forsees large-scale hostilities. Immediate hostilities are far less often noticed the most one could expect to see is a handful of local reinforcements, but nothing on the scale of a response from on of the "Big 4".
The one massive exception to this rule is, of course, Sansha's Nation. While the inner workings of the True Slave network aren't known to us, it's long been an assumption (reinforced by the pre-Incursion Live Events) that most, if not all, of the Nation exists within a single cohesive hivemind; in this case, it would less be a case of not knowing or caring about some distant action, but calculating that intervention simply isn't worth it.
Whether you still call this a "nation" is largely a question of personal preference, but it should be pointed out that there are instances where actions by one branch of a pirate organization ended up being unsupported and ultimately crushed by those they attacked (see the second of the two instances when the Cartel attempted to sieze a Minmatar system - they were utterly wiped in part because this was a local, not a national initiative, and as such the Cartel at large didn't sent gazillions of battleships to back them up.
*Homogenous, i.e., they operate under the same laws and rules regardless of what particular physical bit of the nation they're operating in.