Why a pizza and not a restaurant meal?
Why a scooter and not a skateboard?
A different set of tradeoffs. Sometimes one wants a limited but easy thing instead of a powerful thing that requires significant mastery to handle.
Both Go and Rust and general purpose languages. You can write most (but not all) kinds of software in both of them so a claim that Go is more "limited" than Go is bs.
As to "mastery": I've spent significant amount of time mastering C++ and got pretty good at it.
Go was both significantly easier to master and I'm significantly more productive in Go.
So what exactly is the justification for C++ (and Rust) complexity?
Doing it the hard way: anything with a complex domain e.g geospatial applications where you have an exponential explosion of different logics for different types of shapes or modelling medical ontologies.
You can write anything in any language the issue is if you're taking the path of least resistance to do it and how much risk you're exposing yourself too with variable skill levels of developers doing it.
E.g see all the frankenpython implementations kicking around banks and Instagram to use the "simple" language that turns into something much more complex and brittle.
Name a program you can write in <language> that I can't write in <language> is a terrible way to compare languages. That applies for any Turing complete language, but I wouldn't write a game in emacs lisp.
> Go is more "limited" than Go
Assuming you mean "go is more 'limited' than rust, you can write all software in both languages. I'm not sure who claimed it either because both the linked article and comment above you don't.
The justification for C++/Rust is largely the same as the justification for any lower level language: performance. Theres a lot of cases where GC pauses are a no go (pun intended). Well written rust is going to be more performant than well written go. You have greater control over threads, for better or for worse.
The benefit of rust in particular is the approach to memory management, package management, and how hard rust it is to shoot yourself in the foot. Rust filled a gap where people wanted a performant, expressive low level language without the memory hassle that came with c/c++.