Obama 2.0, that's why. Dude is already planning for the future.
He can’t be a literal Obama 2.0, as he wasn’t born in the US and thus can’t be president. Even if we’re talking about a more small-scale Obama, mayor of NYC is a notorious political dead end. There’s a long history of politicians trying and failing to translate being mayor into higher offices. If this some Machiavellian power scheme, and not just bog standard “you scratched my back now I’ll scratch yours” politics, it’s a bad one.