There's productivity at the level of an individual developer, and productivity at the level of an enterprise.

Just because an individual or a small team can be highly productive in say, Haskell, doesn't mean it makes sense for the whole company.

In Finance, the area I work in, the only FP success stories that come immediately to mind are a couple of teams at Standard Chartered for Haskell, and Jane Street Capital for OCaml. And they are notable for their rarity, not because there are plenty of other comparable examples.

My experience is that pure FP languages have enormous individual productivity but that comes at the expense of lower team productivity/collaboration (my experience, even if not universal or even correct, is that in practice they are fairly idiomatic from developer to developer) and maintenance over time can be an issue for similar reasons. For simple systems and system management scripting, I will take the simpler language.

That said, I'd want a very high concurrence system written in a function language over Python any day (gil notwithstanding). But I'm fine with Python not being that language.