I will accept that they may have had other reasons - but I think naked self interest is a huge part of what they did.

What they said they wanted (going off grid to raise their son in obscurity away from the prying eyes of the press) and then what they did (a massive interview to draw attention to themselves) are in contradiction.

Either it was for financial reasons or to increase their profile. They've got more than enough money to live out the rest of their days (without working) in a decent middle class life somewhere. So why aren't they?