Indeed, one does not always need to learn new tools when available tools suffice; the learning energy can be more effectively spent elsewhere.

I only meant to notice that there's no impenetrable barrier to mastery of that, when desired. I don't think that to learn Haskell at a high level is harder than to do the same with C++. The latter just had more adoption for last 25 years, for a number of reasons.

In any case, some (cursory) knowledge of Haskell improved my Java, Python, and JavaScript quite a bit, and is directly applicable to Scala in many aspects.