Extensive work on VW Type 1 (beetle) engines produced a crank where each cheek/CW is a full cylinder.
Even changes in the OD of the CW create turbulence.
Every cross-sectional area or shape change should be profiled as well - no sharp edges.

Appearance is nice, but the people who do the polishing are not engineers or machinists.

Reasons not to offer this as an option:
Huge extra cost
Slows down the production line
They sell faster than they make already