Your psychoanalysis makes sense in the world of corporations and individuals. But in the world of geopolitics, personal feelings don't matter.
This is North Korea telling the world "We still matter. We may not be able to fight you directly, but we can still hurt you."
> 1. No matter how mad you are, being angry is not enough fuel to collect 100tb of data and then leak it out in 25gb chunks. You need motivation to continue, and money is that motivation.
By leaking the data in a slow trickle, they keep the hack in the news. This attack was designed to get maximum attention in the press, because the more we talk about North Korea, the better for them.
> 2. While company security is terrible everywhere, and with enough work anyone can be hacked, it takes a measure of skill and careful planning to pull off a hack like this. This is a not a "we got lucky" hack. It was planned carefully.
You're right, but think about the kind of hack you could perpetrate if you had a $1 million budget to hack a company. You'd probably buy exploits and malware off the black market, modify them for your purposes, scout the network, then trigger your plan into action. Which is exactly what happened here. It's not like NK are cavemen beating rocks together; they are at least as competent and technically advanced as Russian organized crime syndicates (in fact, my hunch is that NK hired Russian hackers to either train their people or carry out the attacks).
> 3. The amount of data, and the selection of which data gets released when, as well as the difficulty overall of the operation, says to me that multiple people were involved in the hack.
I disagree; the data released was designed to cause maximum embarrassment (and media coverage). The hack itself was not incredibly sophisticated - it's not even as complicated as the Home Depot credit card hacks, and not even remotely in the same league as something created by a skilled state actor like Stuxnet.
> A reason why it isn't North Korea: If it was ( either intentionally or accidentally ) it is in NK best interest to either claim responsibility and embrace it, or to prove they didn't do it. They have done neither. This implies that they can't prove they did or didn't do it, because nobody under NK government control was involved.
They can't outright claim they did it; because that would be an act of aggression. They left a trail of breadcrumbs long enough to tie it to them, yet still have enough plausible deniability that countries who want to believe them because they have an ulterior motive against the US can do so. For example, Russia never admitted they shot down an airliner despite damning evidence to the contrary - who you believe simply depends on what side you support for geopolitical reasons. Realpolitik at its finest.