It's interesting to read this nuanced and economically informed take with his more recent post saying we should raise taxes on capital.

See https://www.gatesnotes.com/About-Bill-Gates/Year-in-Review-2...

Reading them side by side, it really seems like his more recent opinion just wasn't thought out, which is surprising given that he clearly thought about the topic 5 years earlier. My guess is he decided to support what he felt was going to be supported by mainstream Democrats anyway, instead of the economically correct views he clearly understood in 2014.