Why are the yokes always turned?

Ron Natalie writes:

Without any airflow over the ailerons, it's kind of hard to hold
them in the center. As soon as the control flops over to one
side or the other, it tends to stay there.

Aren't they balanced such that they have no tendency to turn either
way? I should think the forces on them in a parked aircraft would be
symmetrical.

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