In the case of Go, I can imagine many of its attributes are significant:
- Good concurrency model
- Familiar style for imperative C/Algol-family programmers
- Requires no VM
- Backed by major corporation
- Runs on all major OSs
- etc
Actually, I think I'm changing my mind. I'd put "corporate backing" higher on the list. Some languages have gotten a huge boost by being backed by a major corporation (classic example: Objective-C), and I'm having trouble thinking of a general-purpose programming language backed by a major company that did not become popular (Dart would be my best guess but even that seems to be doing alright).