Why Functional Programming is not more widely used in industry?

The advantages of functional programming appear to put it ahead of other paradigms (like procedural and object oriented programming), yet it seems it still remains associated mostly with academia, if at all.

Because it's hard and non-obvious. Nothing in the real world works this way (including computers). It's mathy, it's hard like math, it's beautiful like a proof, but that only works for the small subset of the population who want to be mathematicians. Maybe there's some brain structure thing where this works better for 5% of the population. Maybe their biologically wired implicit grammar processor in their brain is a little different. Maybe in the next century we'll find a gene for 'functional programmer'. But it still just doesn't work for the majority of people. If it works for you, rock on with that for your solo work or find a group of likeminded people and do something with them, but I think it's just not going to have appeal to most people.

because its not practical and noone wants to write it.

One of the reasons could be that most programming languages do not have immutable datastructures by default, and most students are taught to progam within a "mutable" environment. Isn't of the first things they teach at schools about "variables", symbols which refer to locations in RAM which might change their contents at any time (at languages like C, Java and C#)?

I think Rich Hickey calls this "place oriented programming" ;)

It is funny how mathematical formulas do not have a "return" statement, they are just evaluated. Math doesn't have an assignment operation either.

Because for the vast majority of software, fast to build is far more important than provably correct.

Because there aren’t any batteries-included RAD frameworks in functional languages yet.

Because most undergrad degrees, if they touch on functional programming at all, do so in only a cursory manner.

Because for most purposes a smart CTO will choose to develop a project in a language/framework that’s good enough and for which it’s relatively easy to hire skilled developers over a language/framework that offers some minor technical advantages but will make hiring even more excruciating than it is for widely-used tools.