First, I think functional programming is used more often than you realize. Not _pure_ functional programming, to be sure, but the use of functions instead of o

First, I think functional programming is used more often than you realize. Not _pure_ functional programming, to be sure, but the use of functions instead of objects is found in tons of real-world software. Now, as to why pure functional programming is not used, well it's the same reason why pure anything is not found much outside of academia, or why there aren't always unit tests, or why there is still lots of procedural programming. The software gets written in a hurry, by lots of different programmers with different levels of experience, and they do it in different ways. Some of them use a functional style, and some use objects, and some use bubble gum and duct tape.