Perhaps because Java is a mess? Much easier to hire? Where? In some locations there’s a 2:1 to 4:1 of C# over Java ratio for demand. And your “why not just use” something else is kinda condescending. You do realize that’s not how one is supposed to choose their tech stack?

Java is “controlled” by Oracle. Kotlin by JetBrains. Scala is “controlled” by… no one knows. Go is “controlled” by Google. C++ is “controlled” through representatives of a consortium of blue chip corps, including MSFT and GOOG. They also “control” Linux to a significant extent. Their employees contribute to many OSS projects.

There’s no perfect governance structure. .NET has the .NET Foundation, like Haskell (also “controlled” by Microsoft until recently) and Python; but who “controls” Python? Did you ever bother to wonder or was it ever important at all?

And the language alone is insignificant, you need a community and an ecosystem that you and your project fit best in and you can rely upon for the lifetime of you project.