Yes, definitely this. So many jobs are found through referrals and networking, especially for non-mainstream tech.

That said, I was pleasantly surprised recently by a search on LinkedIn for Clojure and found some big household names hiring (including several large banks who most people think of as being very conservative).

I don't know, you could say the same thing about more popular languages as well. Lots of people get jobs in Java roles from their personal connections. The difference in postings between Clojure and more mainstream languages like Python and Java is multiple orders of magnitude. Clojure has about 500 job postings on LinkedIn in the united states. Compare with Python which has about 750,000, literally 1500 times as many jobs.

The number of roles in all of Canada for Clojure is about 40 on LinkedIn, easily less than the number of applications a job hunter could send out in a day.