Mhmmm. Yeah I wish the default were to not use a proxy. Though to be fair I'm not sure exactly what the performance implications would be.
The other problem is that it's Google so their perception of "not much traffic" is "biblical floods" to other people.
You can run your own proxy service if you want. There's a large benefit to the go community as a whole for there to be a shared default proxy service.
This is a consequence of what IMO is another bad decision by the Go team: having packages be obtained from (and identified by) random github repos, instead of one or more central repositories like Maven Central for Java or crates.io for Rust. The proxy ends up being nothing more than an ad-hoc, informally-specified, bug-ridden re-implementation of half of a central repository, to paraphrase Greenspun's tenth rule.