It doesn't really matter if you made a horrible uncomputable mistake deep inside a pure function, if you either discard or never use that mistake you would never notice it happened.

For example, nixpkgs (in nixlang) for sure isn't "strict pure FP" - you can do effects whenever you want - but will often have uncomputable evaluations in it. And you will only notice they're uncomputable evaluations when you try to use them. There's even a warning left for future wanderers for that:

    ### Evaluating the entire Nixpkgs naively will fail, make failure fast
    AAAAAASomeThingsFailToEvaluate = throw ''
      Please be informed that this pseudo-package is not the only part of
      Nixpkgs that fails to evaluate. You should not evaluate entire Nixpkgs
      without some special measures to handle failing packages, like those taken
      by Hydra.
    '';