The problem is that there just aren't that many people who choose to invest in learning Haskell -- or for that matter, the essential-to-master nooks and crannies of Rust. And the learning curve to get there is intrinsically steeper that for, well, all those "dum-dum" ducktyped and/or mostly procedural languages one imagines you don't particular care much for, now do you.
Of course it's known that some shops, like Jane Street, have gone whole hog on FP and have managed to do all right, it seems (even arguing that "the fact that the learning curve for our bread and butter is significantly higher than for the usual college-taught languages is a feature, not a bug").
That may work if have the same brand recognition (not to mention salary and bonus pool available) as Jane Street. And even then, it's not exactly proven that large-scale FP worked out so well for them. Just that they didn't tank.
But if you don't have their clout and resoures... from first principles, you should probably think twice before making the same bet that they did.
But as for "keeping quiet" -- that they aren't doing at all. They are (or at least were, when I last paid attention to this stuff) extremely forward about their belief in FP as part of their secret sauce for staying ahead of the competition.
Which, ironically, makes one further question whether it has all that much benefit. Because if it really did ... yeah, they'd probably want to keep quiet about it. Like any other truly winning strategy in their arsenal.
The main thing that I find frustrating is that the actual act of programming in an impure language is so much harder. Haskell is def harder to learn, like 10x at least imo. Especially for a mainstream dev. But, once you know it, there is a simplicity to what you're doing which is very easy to do. I find myself having to just think so hard when writing python. "what exacty does this function do? Oh it calls this other function, I have to go check that one." etc. And then with a myriad of control flow issues, and random syntactic "sugar" to contend with...
There are a number of haskell companies, not just Jane street, and they do pretty well. If you don't follow the space closely, it is not surprising that you don't know about it. But there are. Not nearly as many as Python or whatever, but the appeal to the popular is def problematic: mostly because, at one point python itself was a radical new thing, full of skeptics like "if its so great, why don't more people use it".
Many ideas from haskell/typed fp are slowly making their way out into the larger community. Witness Swift, Kotlin, Java, numerous features in C#, etc. People like them.
Its fine if you don't like Haskell and don't want to use it. But its not an insane choice.
Haskell community really needs to do better at making it easier to get started though. Eventually I hope to contribute to that.
Honest question - does Haskell have such a compelling framework driving its adoption? Or does Haskell suffer the "curse of Lisp" and people just create whatever they need when they need it and no big framework ever gets developed that drives adoption?
Which is not an extra but in fact means a heck of a lot for a language's chance at long-term acceptance.
Sadly no. There are contenders for this that have arisen over the years, but we don’t have a RoR for Haskell yet.
If you’re curious, here is a talk that goes into this problem. It’s very accessible IMO. https://youtu.be/fNpsgTIpODA
To be honest, the compelling reason to learn Haskell for me was so I could engage with various academic literature. I just kept running into things I didn’t understand which were tangential to the topic of the paper, and it seemed like the most straightforward way to solve this was to start with learning Haskell. Once I learned it, I realized I was wrong in my biases, and Haskell is a fantastic tool for normal programming, with some important caveats.
I'd put money on either the team not knowing Haskell when they started, or the "genius" was one of those completely impractical people who do type-level astronautics in Haskell.