This is all true. But then, if you ran HN and needed to hire new devs, you could find them extremely easily just by posting on your own site. HN is a well-known project that people would want to work on because it looks great on their resume and gives kudos when talking to other devs.

In other words, HN does not have the problem that you are going to have if you use an unpopular language for your project.

If you choose LISP for your not-HN project, then you have a problem. The chances are very slim of finding any experienced LISP devs who are also in your salary range, within commute distance, want to work on your project, are a good fit for the team, etc.

You're probably going to have to hire a dev who is a good match on all those other things and train them up on LISP. Unless they've had experience with other functional languages (not that unusual, but not common either) then they're going to have to learn an entire new paradigm. All of which means that they'll spend the first six months going slow while they learn, and needing support from the rest of the team.

And you'll need to convince them to join you (probably by paying them more money) because if they spend a few years on your project learning LISP, they probably won't be able to use those skills for their next gig, and their current skills in a popular language will go out of date.

LISP is a great language, and if used well it will probably give you an advantage over the competition using other, more mundane, languages. But is that going to be enough of an advantage to counteract your slower onboarding, higher salaries, and greater recruitment workload?