Maybe this is a success story: someone made a useful tool in a weird language and we used it successfully for at least a year. Maybe it wouldn't have been made or would've been worse or more expensive if they'd been forced to write it in a supported language. Maybe it would've needed to be rewritten anyway.
My view is a simple one; as one of the leads responsible for it, it was a special case bit of code, something people tried to avoid touching. Nothing about it required a niche language technically, so the added difficulty of working around that was friction and risk. It wasn't that people couldn't learn the language; they could, we had lang PhDs. It's just better if you can keep people where they have existing expertise, and spend your learning points on solving problems users care about.
In contrast, for secondary products, there's a good chance most developers will never work on it at all, and of those who do a significant fraction will spend only a trivial amount of time. Adding the overhead of working in a new language to that balance is significant.
Therefore, the ideal is "Choose the best language for your main product, then write all supporting software either in that language, or a widely-used lingua franca like Python".