Functional programming is basically maths, it solves the problem of how to compose software safely. I struggle to understand why anyone who really cares about their craft would not want this. In fact, many want it so badly they are willing to make sacrifices for it (performance, esoteric languages).
That is working under the assumption that “the benefits” are actual benefits.
IMO, “the benefits” are measurably drawbacks, and not a technical debt I am willing to accept for no good reason.