Because (static) FP is built on a sound and rich theory (type theory and lambda calculus) unless other language paradigms (e.g. OO). There are also different approaches, IMHO:

FPL research: Ok, we have this cool way to describe our computation. But how can we efficiently map this to the HW? In essence build a nice language and find an implementation.

Imperative PL research: Ok, we have this HW, how can we build an expressive PL on top of it? In essence build an implementation (the HW) and find a language.