My guess is that he gave in to peer influence from his wife and daughters. Jenna Bush works for NBC. That tells you everything you need to know.
Bush was disliked during his presidency. Now he is finally getting approval from mainstream media. All he has to do is to badmouth President Trump.
Yes. W really got me when he voted for the most corrupt politician in the history of the USA instead of Trump. That said a lot about what he really thinks of the country.