You don't know what you're getting yourself into with this question, since it might get political very quickly, lol. I am not blaming you, though, we all deserve to know.
One opinionated developer kept telling me that since the humble days of emerging programming languages, a certain company had launched what he called "an attack" on functional programming, and that made OOP prevail. OOP is taught in schools, and usually is the first encounter any new programmer encounters, making them clinch tight to it. That is all to say, OOP is popular because a business wanted to push their product, not because it was better.. That is one opinion.
My opinion would simply be the practical use cases for functional programs are less. Multi-core smart phones aren't new at all, and most frameworks we use to build products are still stuck in the single threaded era, making functional programming less appealing. After all, in functional programming you are incurring a lot of copying thanks to the immutable state of the objects, it might be pointless in a single threaded environment.
Another thing about functional programming that I found annoying was scripting. I love Elixir, but I'll probably use python for scripting small stuff forever, since it's just so easy to preserve an object's state. Or, maybe it is easy for me since I grew as an OOP developer, who knows?
I would like to conclude with a reference to PHP. People love PHP, others wanna burn it to the ground. We can at least agree from that, it doesn't beat other languages in its field if that's the case, and yet... It's super popular.