To be effective in Washington you need to understand the inner workings of Washington. As much as people like the idea of a "Washington outsider" as president, it remains a terrible idea. As much as I LOVE Barack Obama, he wasn't an effective Washington politician. Partly because he was too inexperienced, but probably mostly because he didn't have the stomach for it. Imagine how great a president he could have been with the Washington skills of a LBJ. This is one of the main reasons why I always supported Hillary Clinton in both 2008 and 2016. I believe she did have the skills, insight and stomach to be a highly effective president.
Gates has lived in "Washington" the majority of his adult life and has been extremely "effective" at his job.