The latter are simple in that they're built around a few core concepts which are available to the developer, almost any tool the language designer had is available to the end user. They're simple in the sense that old school legos or meccanos are simple.
Go is simple in the sense of simplistic, it provides a much larger number of restrictive features and most definitely doesn't give end-developers access to the language designer's tooling. It's the simplicity of playmobil or duplo: the developer is provided with much more concrete (and effective in a way) but much less flexible "primitives".
And this is no secret, there's a pretty famous quote from Rob Pike explaining the design and purpose of Go:
> our programmers are Googlers, they’re not researchers. They’re typically, fairly young, fresh out of school, probably learned Java, maybe learned C or C++, probably learned Python. They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt.
Making codebases look uniform and preventing building abstractions (by the language being actively hostile to abstractions which are not built-in) is in line with that.