It's not just cultural. Writing idiomatic C# does not mean you'll write idiomatic Javascript. Nor does it mean you'll write idiomatic Python. Being in the .NET

It's not just cultural. Writing idiomatic C# does not mean you'll write idiomatic Javascript. Nor does it mean you'll write idiomatic Python. Being in the .NET ecosystem exclusively can also mean a reliance on IDEs and .NET-specific tooling to be productive (or things like Eclipse refactoring for Java). And there's the simple fact that there are a lot of qualified candidates who do more than just .NET/just Java. Polyglot programmers are more likely to be flexible and be in the right environment. Of course people can be good enough, but it's not just about the looks. Things happen differently depending on the tooling. Now, the extended part of this discussion is that maybe it's fine, and companies should be able to onboard people into a technology. Because, hey, it's just programming right? But that could mean looking at a multi-month training session until you're looking at someone as productive as the guy who's familiar with the tech already. Not all experience in programming is equivalent. An aside: I feel like this discussion usually has a lot of "web programming is easy" undertones (it hasn't been explicit but we all know what "trendy" means). But I don't think there would be as much of this discussion if it were something like "web-only developer applies to work on embedded systems with basically no C experience".