1. A lot of people actively want to use Haskell, more than there are Haskell roles. Nobody is going to jump onto a generic Java role for the sake of using Java!
2. Language choice is a way to show rather than tell that you are willing to do something different and interesting. This ended up mattering even to non-Haskell candidates—I remember one very qualified OR expert told me he chose us over Google in part because the Haskell/PL angle to our approach sounded a lot more interesting.
When I later moved to a more traditional data science team at Target, the difference in recruiting was pretty striking. I used to field qualified inbound candidates all the time, while the new team rarely got any; the recruiting pipeline was noticeably spottier; when we did get qualified candidates, they were more likely to reject our offer. Programming language choice wasn't the only difference between the teams, of course, but it was probably the most externally visible difference to candidates.
With this experience, if I ever go start a new team or company, I'm going to use Haskell as a secret weapon to make hiring much easier. That goes against tech industry "common wisdom" but, as ever, common wisdom is far more common than wise.
This was about five years after industry representatives argued that my school should stop teaching C or C++ and focus on the more modern Visual Basic. They explained that, by the year 2005, there would be more COBOL jobs than C jobs. Meanwhile, a semester of Visual Basic experience would guarantee the students a lifetime of employment without learning a new language.
I'm under no delusions that Haskell will be the next Python or that Python itself will go the way of VB, but it always makes me take these "industry" arguments with a grain of salt.
A language like Haskell is much easier to hire for because you can get higher quality employees at a lower price, due to the high demand for Haskell programming jobs and low supply of such jobs. If you got for a language like Java, a double digit percentage of the candidates are the kind that can't even solve fizzbuzz without help, so you have to waste much more time weeding out mediocre candidates.
I worked for a Haskell consultancy for 7 years and did hiring interviews. We filled open roles extremely quickly; the biggest problem was to decide which of the multiple high-quality applicants to pick.
I am now running my own startup and we just put out an internship job description [1].
Within 1 day we got over 20 excellent applications, and we'll probably have space for only 1 for now.
Maybe if you want to hire 100 Haskellers on the spot, you'll find hiring difficult. But most starting businesses don't have that problem.
[1]: https://old.reddit.com/r/haskell/comments/vklj9d/benaco_offe...