why dont the shells of the atom distort because of the attractive forces between the protons and the electrons

Answer 1

Because of the symmetry. The shells are basically pulled straight in.

Answer 2

It all has to do with the solution and physical reality of a set of waves that allow the electron to orbit the nucleus without collapsing into it. From the perspective of an orbiting electron, there is no preferential view of the nucleus (Symmetry as mentioned before). There is no reason that any distortion should occur.