I would imagine it's difficult to stay deeply involved in something like that with one's ex.<p>People get divorced for many reasons but generally they don't want to be around each other any more and being co-chairs of a big foundation would make that pretty impossible. Business (or charitable) partnerships are like marriages in a lot of ways.
I was wondering and found this in the article:<p>> The organization’s name will change to the Gates Foundation, with Bill Gates, her ex-husband and Microsoft founder, becoming the sole chair.