You don't polarise electrons, you polarise the molecule. The distortion of the electron density depends not only on the applied field, but also on the field due to the nuclei, and its orientation relative to the applied field.

Have you studied symmetry? If two directions are symmetry-equivalent, the polarisability in those directions (or any direction in the plane defined by them) is the same. For tetrahedral, octahedral and icosahedral symmetry, all three directions are symmetry-equivalent, so the polarisability is orientation-independent.