It has everything to do with people's perspective of the world: rich people cannot be good people. If you gain something, somebody else needs to lose something. So for a rich person to get rich, he must have taken a lot from other, "nicer" people.

Bill gates must really love swimming "uncle scrooge"-style in his billions. That's all he cares about. Everything he does must be to gain more billions, so he can swim in a bigger pool.

Bill was also super competitive, so let's focus on that and forget that he made his money providing value to users and businesses. It's better to act like he stole the money in an unfair way.

I personally feel very sad for a person that can't imagine that someone else could feel happy and satisfied by helping others, by having a huge impact on peoples lives in a positive way. I'm sure Bill and Melinda get more satisfaction of helping other people than looking at numbers on their bank account. But hey, that's not possible because he's rich, and therefore evil.