Not going to imply he stole, but rephrasing the question as why would someone really rich want to steal?

Greed.

It's why politicians who have enough money for several generations continue to take more and more bribes. (I live in Sri Lanka and witness this on a regular blatant basis).

Enough or more than enough isn't a reason for human nature to not want more. It actually seems to be a driver to get more by any means. (my assumption )