I've never seen someone succeed at giving an objective explanation. Anecdotally and subjectively, functional programming is a different type of thinking about a problem... Instead of breaking it down into stages, I'm almost breaking it down into a graph and figuring out how the nodes must connect. LISP is also like this.

I wouldn't be surprised if cognitive modeling shows that graph-manipulation engages different chunks of one's brain than step-by-step procedural description, but I do not know.