Language is rarely something people swap between willy-nilly. What you can do in Java, C, C++, C#, Rust, Elixir, etc. you can do in Go.
Some might have strengths and weaknesses, but if your business is a website or a web technology and you're already using Go, then what problems are you likely to face where any other language is a better choice?
The only thing I'd reach for a different language than Go is if I wanted to develop a GUI. I'd go for Java, C# or Rust.
Management (and other developers) don't look highly on someone suggesting a different technology stack for each problem you encounter. You'd really need good justification to use it.
New languages means developer training, potentially harder hiring, some developers won't want to learn it, knowledge can easily be hoarded by a select few individuals and lost easily, etc. It's not a position you want to find yourself in every few months.
I was paid to use C# before I was paid to use Go. Everything I do in Go could have been done in C#. We moved to Go because it was a nicer fit for our team in the long run, but it wasn't an easy task to migrate an entire team to Go. I could not imagine having to maintain multiple tech stacks because someone thinks Rust is a better fit for a specific task and another person thinks Java is.
It's not cargo-culting, it's called being a developer. I'm not paid to be a jack of all trades. I'm paid to develop Go applications and do it well. I'm not a fan of having to learn new languages each year. Keeping on top of .NET is already a pain, I'm not going to do that for 5 other ecosystems.