Well, some people like the decisions behind Swift, and would prefer a language with an ecosystem, documentation and developer community of the size that results from Apple being involved in it compared to, say, Jane Street.
Heck, people also use Go mostly because of the Google involvement (and the momentum that gives), and it's a language 30 years behind Swift.
Interesting idea. Can you post a link that explains why that is?
Now, Swift is pragmatic too, and far from cutting edge, but still ways ahead of Go in that area, and its creator is a very strong player in the field of compilers (he also did LLVM).
Here's a link that shows how much hasn't changed:
And .NET only had value in the MS world before Mono which very popular.
There is hardly any modern Mac application that you can compile with it.
Which is why they are making an open source version that will have value in all ecosystems.
Swift without Cocoa, UIkit, GCD, Playground, IDE support..., doesn't offer anything better than those MLs.
Swift only has value with the Mac OS X and iOS ecosystems, specially as a mean to drag Objective-C developers into the FP world.
There are so many open source languages in the ML family, a few of them are even used in the industry for several years now. Just go and join one of those projects.
They will appreciate any help they can get.