"S" shaped tonearm ?

Better geometry so that the tracking angle is improved over more of the record, I think.

One can get the proper geometry by just bending the head of the arm (like most tonearms), so that is not the reason for the S-shaped arm. I believe that the S-shape is an attempt to balance the mass of the arm about the axis drawn between the pivot and the stylus. Without the S-shape there is more mass on the "outside" of this axis. Why such static balance along that axis is important is not clear to me (aside from reducing torque in one direction at the pivot). The "cost" of such design is much more mass. For any given mass, other designers would favor increasing the rigidity of the arm instead of trying to achieve such balance.

I think it was a combination of improved geometry and "sexiness" of the s-shaped arm. It was a way to stand out from many other mass market products (which of course got picked up by the mass marketers). Just MO.