Try riding with your front wheel in some kind of rut that prevents steering. You fall off if you unable to steer. If we are contantly making small adjustments to the steering, we are not riding in a straight line. It just appears straight because the radius of the curves is so large. Most complete newbies attempt to steer a straight line and wobble all over the place. If you direct newbie to ride in curves, around some widely spaced markers then balance becomes a lot easier.

Training techniques often seem counter-intuitive because experienced people forget or internalise what they are doing.