Like I said, Windows support is currently middling. I would bet there's some Linux production code in Swift, though not much. But both of these are cultural problems, not technical ones. If Apple said tomorrow, "we're going to go all-in on making Swift a universal programming language", thousands of developers would cheer and jump on-board. The main thing holding it back right now is lack of confidence in its support; people don't want to invest in a new cross-platform codebase that might have its legs cut out from under it in a couple of years.
Swift is much closer to the metal than .NET, and it has very innovative syntax features. It's more analogous to Rust than to C#. .NET is a strong cross-platform ecosystem, but it's silly to say "we don't need any others because this one's good enough". It's not even the strongest one that currently exists - probably the JVM is. It honestly just sounds like you're hating on Apple for the sake of it.