My theory is this.
The press, and to some extent the internet in general, functions the same as a narcissist. Building you up with knocking you down already in mind, especially for women. Spreading untruths, picking you apart
The natural reaction is to want to defend yourself, dispel the lies, set the record straight, say no, this is not what happened, to right the injustice
When learning about narcissists we are taught to respond rather than react. Responding is very dry and emotionless whereas reacting is emotional. The emotion and upset is what the narcissist (the press) wants
We are also taught that often the best thing to do is just to let them say what they want, know within yourself that it is untrue and don't get caught up the spiral, the web that they want, especially not emotionally.
While there were a few moments of emotion in that interview, an overarching amount of it is response rather than reaction, and they have done such a dreadful, despicable number on Meghan that I don't blame her and Harry at all for wanting to respond.
I think all they wanted was to simply put their side forward, calmly, which is what they have done - and with clear affection for the actual queen and family, the hurt clearly came mostly from the outdated dinosaur of an institution and protocols, the advisors surrounding the family, and the absolutely vile nature of the press
They come across as very fair and even. They were not paid. I think that fact paired with their conduct during the interview and careful responding rather than reacting speaks volumes