Nobody here wants to say it, so I'll just say it and face the downvotes...

JavaScript as a server-side technology sucks. It was cool back in 2010 when NodeJS first came out and event loops were all the rage. But .NET is now 10x faster than NodeJS, statically typed, has better community support, better tooling, broader official libraries, better package manager, and as a bonus it's not JavaScript. The productivity and performance of .NET with Visual Studio is just unmatched.

Because it's nice to have all tests in a single view and a single language, both unit, integration and end to end.

Also regardless of keeping it in a _single_ language or tool, one might prefer to write tests in a .net language instead of js or python.

This doesn't apply to javascript as much, but might again one day.

But yes, spending my weekends learning a new language and library is not a feature.

I'd much prefer to spend my off time learning more about my target users, how to better manage a team, or the legal regulations surrounding the domain I'm writing code in, or just hitting the gym...

Not to mention as soon as I add a new language to our project stack that means every current dev has to learn a new technology, our build pipeline becomes more complex, we need a second set of coding guidelines, and finding new devs becomes more difficult because they'll need to know 2 languages instead of one or we have to increase the onboarding time for every future dev who roles onto the project.

I think it's uncommon that it's worthwhile to invest in a second language/tech stack on a real project.

Well, a pretty good reason is that C# is statically typed, which a lot of developers prefer. It's arguably a much more powerful language than JavaScript too.

Personally, I work with both C# and JavaScript, and I'd happily use the C# version of Playwright to write and run UI tests.

Why not?

Why do You think that this will somehow limit people ability to learn or even make them worse version of them?

Most of the dev's I know, want to do coding for life: - not learning tools from scratch every few weeks, because of the abandoned library - not fight with npm audit every week - not waiting for 5 minutes for webpack to download internet and build project in CI, while .Net builds are already completed, unit tested and waiting for smoke run.

Projects written in java/c#/python don't have to write their own ad-hoc http api in nodejs to access playwright from their language.

Because the “Enterprise Architect” who hasn’t done any actual coding in 15 years, and still preaches 15-year-old FUD about open source, will be openly hostile to anything that isn’t superficially related to his anointed tech stack. Which will most likely be either .NET or Java.