Back when I worked on a large commercial Python project, we did the same thing. All dependencies where on our server and that's the only place we grabbed them from when building a new release.
I think the main problem is that we got used to these dependency tools, and many developers coming to Go don't have experience how development was done before they came into existence.
Or the fact that many developers look at the previous methods and quite rightly say "That is a hideous method, we have moved on (and IMHO improved) from that, why the hell has a new language reverted to old and busted methods"
As I said in another comment regarding Go. If any company has the ability to create a stable, maintained CPAN / rubygems equivalent for the Go language, it would be Google.
Which just makes the lack of it more jarring (although I see the arguments that Go is designed for Google and may not fit other's ideas of what important features are)
