In fact there is more reinventing the well in go because all the std lib is just that… a library. When you need all the fluff around parsing routes, validating objects, preventing XSRF and a multitude of common solved problems, you have to reach for third party.
I also don't agree that one is 'reaching' for anything, since as soon as you interact with the broader world of interconnected systems, most of the first-party Microsoft things just don't work. They are almost all designed for their own standards that are too different or have to be manipulated too much to be compatible with something else.
Some things don't even exist like a basic Redis client. At that point even a highly experienced Microsoft developer has no choice but to get that non-first-party library.
dotnet tries to do too much by itself and that makes it annoying to use unless you happen to be building what it wants you to build.