The problem with the lack of adoption argument is that the only paradigms that saw widescale adoption was imperative and oop; its difficult to imagine that we as an industry picked so well on the first try (imperative) that only oop could compete, and even then is treated as an extension of imperative than full-on oop. Especially when its easy to imagine viable reasons for the paradigm's success not based on merit: inertia, market economics, network effects, luck, piggybacking off unix's merit, ease of learning (compared to previous major languages), etc.

Hell, even as you claim, libraries/communities is a chicken and egg problem, and its certainly easier to build a community on a familiar language/paradigm, than a different one.

Its a big ask to assume that it boils down to productivity, especially when most alternatives are completely unknown to most: imperative, oop, and recently functional are the only options non-academics would usually imagine. Concatenative, stack-based, logical, etc are gone from the conversation long before productivity ever comes into play.

At best, the productivity question is likely just a short term one: it costs little up-front to jump from C to Python, compared to C to Haskell. The long-term productivity question is more likely than not, not actually in play. And presumably even haskellers don't think of a proper comparison against C, in the long-term benefits (they'll usually note C's weaknesses against haskell's strengths, but not vice-versa; the C programmers will do the same in C's favor)

The pure-functional features have gradually been adopted. It's hard to imagine a new general-purpose language coming out without map/reduce/filter, or without some form of typing with generics and inference, or without pattern-matching. It's hard to remember that these things were all seen as pure-functional nonsense a decade or two ago.

I'd argue that the more pure FP languages have a higher learning curve, but that doesn't equate lower productivity. Plenty of people are productive in FP languages, and there are a good number of FP languages with decent adoption throughout the industry. They might not be as widely adopted as Python, but that's because it's really easy to learn Python.

...is precisely the attitude that killed perl.

I don't want the extreme strictness of haskell or F# but I'd rather be edging in that direction rather than edging in perl's direction. 572 was definitely the latter.