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.

There might be a particularly strong Green/Brown delineation with those, with programmers loving to write code in them, but disliking to maintain other people's code.

Scala and Haskell are also in the most loved languages, why do you think there's a lot of hate for them?

I think some people feel productive writing lots of code, while others feel productive learning ways to avoid writing lots of code.