[CrimsonCape]

I think the explanation is the fundamental reality: computers are used to transform data, to store data, and to present data; FP determines that two of three reasons are impure and must be minimized.

John Carmack says that FP is a hinderance when rendering graphics, working with buffers, etc. So in respect to presenting data, UI and graphics will likely always be in an imperative lang.

Rich Hickey's (creator of Clojure) company Datomics (i.e. proprietary) uses his design for an immutable database which has only been around since 2013. He says that disk storage was so costly in the past but is now so cheap that the existing server industry is built atop this legacy of old ideas. So FP regarding storing data is likely in infancy.