I think functional programming is less popular simply because people just aren't good at it. Functional programming is a good way to describe how a system work

I think functional programming is less popular simply because people just aren't good at it. Functional programming is a good way to describe how a system works. By describe the input, the processing, the output. You describe the whole diagram. However, in reality. People just sucks at thinking systematically. It's likely that the whole education system never taught you about how to do it. Everyone was taught to do things step by step and smash the results together to see if it works instead of prepare everything before doing any actual work most of time. And if it actually need preparing, there is usually a pre made checklist for you to do it easily. That type of thinking process isn't that common in our daily live. And of course no one is used to it. But I think people should at least do it once. Even you are still programming interpretively afterwards. It could benefits you very much and make you a better programmer.