I've heard it's seen limited adoption in finance.

https://github.com/interregna/arraylanguage-companies

I mainly work in financial markets. I have personally seen it used many times in some places at most of the places I have worked at. KDB/Q is an important component for historical data and order capture here at OSL. The only issue I have is there are few developers and they cost a lot of money. We are lucky we have a very good one.

How much is "a lot"?

APL came out a LONG time ago and was sold by IBM for awhile. If you look for Dyalog's customers you'll see some recognizable names. Volvo has their entire inventory system in Dyalog APL or something like that if iirc. Kdb+ is used a good bit on Wall Street and also by F1 racing and a few other places. I'm sure J is in use somewhere, but it's probably a bit rarer.

https://www.dyalog.com/case-studies/hercules.htm

APL had non trivial uptake during its heyday.

J is apparently somewhat popular with actuaries and similar.

K/Q is used by a number of finance companies, via the KDB vector database. Here the selling point was that the overall system was great for in memory vector processing of stock tick data.

Arthur Witney also built a language named A+ while at Morgan Stanley that was used in production as an improvement over various previous APL apps.

They're odd languages but have found successful niches.