Which a lot of libraries are doing because they wrote an http.Transport{...} literal in an earlier version, and then std added new fields to the type in a way that silently breaks existing users. The zero value should have matched the previous default behavior.
Case in point: https://github.com/prometheus/client_golang/pull/1885/change...
We had the same in our own library, and now have a testcase checking if our own custom instantiation of http.Transport matches http.DefaultTransport, so that the tests scream loudly when upstream pulls this shit again: https://github.com/sapcc/go-bits/pull/309/changes