If you don't make type mistakes, good for you, but why not let the compiler or interpreter provide a safety net, just in case? In addition, static typing makes refactoring easier because you can confidently redesign your code and let the implementation tell you which types you haven't yet adjusted. Besides, type inference means that you do not even have to write out the type yourself in many cases. (However, to do so is better for documentation.)

Also, why do you think that Microsoft is secretly pushing static typing? /Maybe/ it's shilling for TypeScript, but there are a lot of other statically typed languages that compile to JavaScript, such as Elm.