Go seems to be an iteration of Rob Pike's previous languages, Limbo and Newsqueak - perhaps with a sprinkling of other ideas, but not much.
Rust on the other hand has been a far more ambitious project, with very lofty goals. This has meant that the Rust team has needed to do a huge amount of experimentation and iteration, culminating in the tight set of core semantics that you see in the language today. It's not been an easy journey for the them, but a great deal has been learned in the process, and even if Rust never 'makes it' into widespread usage, its contributions to the field of programming language design will be felt for years to come.
This is not to diminish the efforts of the Go team - they have produced a really tight, polished language, with an excellent set of bundled libraries. All I'm saying is that they weren't starting from scratch, and had different goals to the Rust team. That has meant they could get to a stable language much faster.
Rob Pike's keynote at GopherCon 2014 does a great walkthrough of the evolution of the design of the language, where ideas were borrowed from and why: https://www.youtube.com/watch?v=VoS7DsT1rdM
That looks a lot like today's Go. All of the major design decisions were made, distinctive Go concepts (slices, maps, interfaces, goroutines, switching on concrete type, etc.) are all present. Most of the code examples would compile today with only a few tweaks (if any).
Suffice it to say that Rust was not in that state in 2010. It was barely in that state by 2014. Go was released as a beta; Rust was released as a pre-alpha. That isn't a judgment of either language or community.
Externally, it certainly seems that Go was open sourced in a far more finished state, with only relatively small tweaks after the initial release, while Rust was quite raw and has had most of its fundamental design work done in the open (with significant contribution from volunteers, both code and design) after being placed on github in 2010.
Rust on the other hand has been a far more ambitious project, with very lofty goals. This has meant that the Rust team has needed to do a huge amount of experimentation and iteration, culminating in the tight set of core semantics that you see in the language today. It's not been an easy journey for the them, but a great deal has been learned in the process, and even if Rust never 'makes it' into widespread usage, its contributions to the field of programming language design will be felt for years to come.
This is not to diminish the efforts of the Go team - they have produced a really tight, polished language, with an excellent set of bundled libraries. All I'm saying is that they weren't starting from scratch, and had different goals to the Rust team. That has meant they could get to a stable language much faster.