CCP has indicated at certain points that ultimately the only power capsuleers are legally answerable to is-- no, not CONCORD; that just gets to blow you up if you're naughty in certain particular ways in certain particular places-- their corporations.
Not their factions. Not their native governments. Not, again, CONCORD. Not even their alliances. Just their corporations.
The hard part about this is figuring out how such an insane policy would ever have become interstellar law. It may be a matter of there being two practical approaches to dealing with capsuleers: strict control or loose control.
If the factions went for strict control you'd have an arms race over who can train the most of them and who can most swiftly genetically engineer the largest percentage of their population to withstand the pressures of training-- among other uncomfortable problems. No nation, for example, could afford to discharge its capsuleer agents without also somehow irreversibly disabling them, lest they be snapped up by another empire, the Cartel, or various other powers with intelligence divsions. And "disabling," in this case, would probably mean shooting them in the head.
The nations would also be directly culpable for various capsuleer excesses, etc. Furthermore, this comes within spitting distance of slavery, a big no-no for the Federals and Minnies.
Loose control has the merit of preventing an arms race and really wants an arms race over capsuleers. All of them want to have capsuleer minions at their disposal, and can get them using the carrot instead of the stick. The capsuleers aren't under anyone's thumb, so no one's thumb gets smeared in the blood of capsuleer atrocities.
Instead of each faction building a destabilizing stockpile of sentient, crazed weapons of mass destruction, every empire (and other faction) has access to a community of what boils down to blood-saturated mercenaries. Capsuleers bathe in sewage and bodily fluids for a few ISK, while the empires come out smelling like roses. The farther the factions can distance themselves from these deniable assets, the better, and how do nations distance themselves farther than to declare capsuleers to be functionally without nation?
The capsuleers become, in effect, the tyrants of a million or so independent, mercenary city-states (consider the number of crew + support personnel involved), legally beholden only to voluntarily-established nations of cooperative cities-- which they can secede from almost at will.
No empire has authority; every case in which a capsuleer is subjected to empire justice is one where the capsuleer voluntarily submits him or herself, or is forced to by a corporation. Naturally, the nations can take certain covert actions to eliminate particularly troublesome capsuleers, but that is a dangerous game indeed, since any slip-up that compromised the operation would expose that empire, perhaps all the empires, as responsible for killing (or otherwise meddling with the sovereign rights of) capsuleers, with unpredictable consequences.
Any middle road would eventually lead to either the tightest or loosest level of control, with a much more resentful capsuleer population with an adversarial relationship to the factions. Hence the present approach.
Best explanation I can come up with.