Naturally the people who know these answers are very busy today but hopefully we will hear more soon.
Whoever is politically convenient
> How?
Probably social engineering but possibly poor security practices
> What vulnerabilities allowed the intrusion
Probably poor security training on employees and poor safeguards, but possibly also poor security practices in software engineering
> what organizational processes created those vulnerabilities?
Leadership with poor priorities and shortsightedness for the sake of short-term profit
I'd be willing to bet that they have comprehensively sloppy and terrible infosec practices and that we'll never hear any details about it - most of their customers wouldn't understand, and it would only expose how bad they are at all of this if they did.
Most of us don't actually know the answer, to be honest. They're not telling 6500 employees what really happened. I know more than you, but not that much more, and I'm definitely not saying anything about it.