It’s part of it in the sense that it’s harder to train the next generation of programmers to use FP. But you’re right that inertia has a great deal to do with it: OOP is well-entrenched in the IT industry. Incumbent technologies are always tough to displace.
There’s no question that FP has its use cases and will be used where appropriate. OOP will continue to be widely used just because almost everybody knows OOP.