Why wouldn't they? It's a very good programming language that's underrepresented in the market. I don't get why people get so upset over language evangelists. Is it that you already know the languages they advertise are good, or that you don't want to know?
It's that, by their own demonstration, the language is nowhere near as good as they say it is. What does "underrepresented" even mean, in this context? It is not used much because it is a PITA to get tolerable performance, where the C code -- and, moreso, the C++ code -- written in the most naive way is near optimal.
I am not going to bother demonstrating the parallel C++ version, but you already know it will be only a little longer than the naive one, and quite a lot faster than the Haskell one.
You're right and Haskell doesn't really deserve more representation. I've built a couple of small web services, a network protocol and a compiler in Haskell, and for those cases it was super suitable, god forbid I'd have to do those things in C++. But definitely, there's a whole bunch of programming languages that would have been as suitable or better for those (except the compiler, Haskell really is the perfect compiler language).
I meant underrepresentation more generally, I appreciated Ruby evangelism back in 2006, when adopting Ruby really improved the lives of web developers. And I appreciate Rust evangelism now, because it improves the lives of zero overhead developers. At some point those languages could be at their "optimal" representation though. And not all representation is fair, I still thing it's insane that people are advocating Rust for web development, but I also think it's insane to use Javascript for backend web development, and here we are with half the industry mired in shit.
Haskell's focus is arguably making correct software, not the fastest implementations. Such intensive focus on correctness is not usual. In that light I do feel it's somewhat under-represented.
Ada/SPARK is underrepresented as well. Correctness? You most definitely got it. Performance? Yep. Easy-to-use language constructs for concurrency? Yep. And so on and so on.
