Same shit happened when he pledged 99% of his stock charitable causes. Everyone was up in arms about how the organization was an LLC instead of a charity, claiming he did it purely for the tax benefits, despite that being bullshit.
I guess at the end of the day, once you are a billionaire for creating a successful company, everything you do is based entirely on greed. I'm sure we can come up with a self-interest reason Bill Gates is spending hundreds of millions eradicating malaria too.