As to why this is the case, I think maybe this is enabled by Go's backward's compatibility focus and encouragement to upgrade early and often, and the community's focus to utilize small interfaces sometimes from the stdlib itself, like io.Reader and io.Writer, or http.Handler. Added to that w.r.t. using the latest and greatest, most Go users frequently are using the latest version of Go even in production (per the go experience surveys).
I am sure it also helps that Google pays people to develop, maintain, and improve the stdlib.