Because skiing and snowboarding are the most important pieces of gear in the big events that are also accessible to the general public? Skates are probably the exception but don't tend to generate that same cool factor in general use.

That, and the fact that they have a big, otherwise unused upper surface. Where would you put a big honking logo on a skaters shoe?

It would also be nearly impossible for the IOC to say 'cover that logo on the base' as you would be changing the sliding characteristics of the ski or snowboard.