Functional programming itself is really old. Practical functional programming for scale is the new trend.

What's new is the scale of software being developed right now. Developers simply can't afford to create mutable and shared state as if their program was just another desktop program, executed on a computer disconnected from the internet.

Sooner or later we learn that focusing on the human value of code (I mean, making the code clear, concise and simple to read) pays off way better on the long run rather than optimizing for CPU cycles or memory footprint.