But, the joy of 2020-era design is that nothing is forcing you to use Go. Everything is coupled with network APIs these days, so you can generate your protocol buffers for whatever language you want and write your chunk in that. You don't have to look at the success of Go in this space, think "but I don't like it", and leave the field. You can do whatever you want. But, I do think it's accurate to say that Go has a lot of mindshare in this sphere of the Universe. It is what it is.
Also, by restricting to open source you dropped 2 biggest and successful players.
I think to get an idea of what mindshare looks like, you have to look at people that started from nothing today. These are the people that are making architecture decisions with an eye to the future, growth, and immediate productivity. When you're inside a huge org, you have to think about what is easiest to integrate with, and what skills you can get from other teams. At a company that's 80% Java, that's Java. It would be insane to switch, and likely to fail.
I think the common thread here, and what separates this from internal tools a la "Amazon is 90% Java" is that these tools are Open Source from the beginning and want to encourage community contribution as much as possible. I don't like using go myself, but even I can't deny that if you're running an Open Source project and would like to encourage contributions from people of different levels of involvement and general programming proficiency, go is one of your safest bets.
> What about ALL the other components NOT written in Go?
Out of curiosity, which components are you thinking about?
I could start listing off OS kernels, and then I'll move on to device drivers and hypervisors.
"The Cloud" is enabled by the fact we can efficiently separate applications and users running on the same hardware. The software which ultimately enables this is not written in Go... or Rust... or C++... or any other "hyped" language, but it is still an essential part of any cloud service.
Those components are either being rewritten in go, or packaged as containers to run on infrastructure that is written in Go.