Well for one thing, sometimes projects are just for fun, or to explore uncharted territory, without thinking about a specific use case. For another, there are definitely use cases for proofs in code, as verified software appears in a variety of domains. It’s not likely to make its way into the average CRUD app any time soon, but that doesn’t mean it’s not useful.
> Haskell is barely used in the first place, and even less for highly safety critical software.
“Barely used” is relative. Compared to java or python, sure. But there are untold millions of lines of Haskell code running in production right now. Besides, in my humble opinion Haskell should be used more, whether or not it is (right now). And in any case Haskell has had a big influence on many other more popular languages, and/or libraries, and this could one day be another example of that.