It's about predictability for oncoming traffic; f*ck the tires and your recovery speed, you already blew your best shot (once it has reached 90 degrees to the desired path, or even less if it has a crappy turning circle). You're correct that the driver won't be able to change the direction of the spin; that's the point.
When a car's momentum is allowed to carry it through the path of least resistance (it always will), factors such as steering angle, polar moment of inertia, corner loading, grip variance on the surface(s) in play, and more are all going to affect whether the car is carried to one side or the other. Ain't nobody got time fo' dat! Locking the wheels nullifies or greatly mitigates the influence of most of these factors.
When cars are bearing down on this situation as it happens, the best thing they can have is a predictable, straight path, around which it is much easier to plan an escape route. Otherwise, it's like trying to predict what the squirrel in the lane ahead of you will do (but Lemons cars are a lot bigger and heavier).
Once the tire is scrubbing against the pavement, the rubber "knows" little difference whether it is along the direction of the tread or broadside; but if not fully locked, the car's trajectory will get steered one way or the other, which too often is back into traffic that would otherwise have cleared the incident, even by a few car widths.
You will not find a racing or high performance driving school that does not advocate locking the wheels (if possible) once the driver has exhausted their control.
