Is it? That seems like a very bold claim. MLs have been at the heart of a lot of language development for the last few decades, both as research languages for various concepts, but also practically: OCaml is fairly famous as a language to write programming languages in. FP isn't something wild and niche, it's discussed fairly regularly even amongst users of mainstream programming languages. Even Go has an FP library now, coming out of IBM of all places.
I don't think you can attribute this to ignorance, because it's very clear that Pike is not ignorant of programming language design - even if you disagree with his decisions, he has had tremendous success at implementing his vision. To me it speaks more of disinterest - FP doesn't seem to really register on his radar as a useful mine of PL ideas. That's fine, although I agree with the previous poster that it's ironic to be such a proponent if APL, and yet have such a blind spot to another very fascinating area of his field.
Would Haskel or some other functional language be a part of a typical CS curriculum?
I remember having a course about programming paradigms which introduced different languages and we wrote a small project based on functional languages.
Possibly. It's wierd he's so enamored with apl which just seems to me like languages focused an algebra designed around arrays.
Algebra based designs can be formed around many data structures and many languages generalize this concept like Haskell. With Haskell you can create your own algebraic DSL around arrays and anything else you can think of. It seems he's enamored with the specific array instance of algebra based designs and unaware of how it's only one specific case of a general concept.
APL wasn't originally a programming language at all. Ken Iverson designed it as a mathematical notation to express and reason about computer algorithms. "Notation as a tool of thought," is how he thought about it. It was implemented as a programming language years after he created the notation in 1960.
An APL-like Haskell DSL could be interesting, but to match APL's expressiveness you'd basically need to reimplement all of APL. For maximum generality, one could just skip both APL and Haskell and just use the lambda calculus. I found that a bit hard to work with, though.
As far as Numpy and all, they are all directly descended from APL. The difference is that it takes 10 lines of Python to match 10 characters of APL. While the array languages' terseness can be excessive, doing it in Python is not very pleasant either.
I don't think you can attribute this to ignorance, because it's very clear that Pike is not ignorant of programming language design - even if you disagree with his decisions, he has had tremendous success at implementing his vision. To me it speaks more of disinterest - FP doesn't seem to really register on his radar as a useful mine of PL ideas. That's fine, although I agree with the previous poster that it's ironic to be such a proponent if APL, and yet have such a blind spot to another very fascinating area of his field.