while it's true that usually, you need to understand the basics of CS to write good functional code, we've often found that that doesn't need to be 100% correct.

we've placed a good amount of functional engineers from a Math, Physics, Logic sometimes even Biology background that had a strong affinity for functions and found OOP generally painful.

I think it's that functional programming is more of a niche with an even more disparity between demand/supply regarding the salaries.

Oh, and usually HR people have a pretty bad filter when it comes to functional engineers, so they only filter by keywords