While Google's support was definitely a factor, Go also had some important language features going for it. Most importantly it is targeting a relatively empty niche in the programming language landscape, i.e. that of high performance, close to the metal languages with little performance overhead, while still being easy to write. "Easy to write" for 80% comes down to being memory-safe, unlike C/C++. If you're in that niche, you have few alternatives. The other options for mainstream memory-safe languages are interpreted scripting languages and Java-style jitted languages. Go easily beats both in resource consumption without being much harder to program in. Rust isn't really comparable because while it is memory-safe its memory management system still forces the programmer to think about the memory and resource usage, thus being slower to program in.

I have always used Pascal for that

But no one else does

Go is just shitty Pascal, change my mind.

On a more serious note. I decided to read Delphi documentation recently because I’m old enough to hear a lot about it, but not quite old enough to write anything in it. It had discriminated unions. It did! I can’t imagine my life without them, I write stuff exclusively in Ocaml-like languages, so the only question that I have in my mind is “how the hell we managed to go backwards?” It’s so weird.

Go has some restrictions, but all in all it's a great little pragmatic language, which solves a lot of practical problems (utf-8 strings, concurrency, garbage collection, cross compilation, single binary deployment, performance, readability) and which I can easily keep in my head as opposed to most of the other languages I've used in my career.

In that way it's like a Delphi for the modern world.

No, Free Pascal is Delphi for the modern world.

Of course it had. Turbo Pascal had, AFAICR. (Probably because, at a guess, Wirth-standard Pascal did; though I'm less certain about that.)

How is that different from eg. D? Or the myriad other GCd AOT compiled languages?

Did google still have fans among the technical crowd when golang launched? I'd expect Rob Pike and Ken Thompson to be the fanboy-attractors rather than google.

What happened to Dart, then?

It got betrayed by Google itself when the Chrome team dropped support for DartVM support.

Then AdWords team which had just gone through GWT => Dart rewrite, kind of rescued the project from closing down, after the key designers left.

Finally Flutter team kind of gave a new life to Dart, which made Dart only relevant in the context of Flutter.

It targeted the front-end, which lots of programmers don't give a shit about.