[MichaelJ]

The straight pole is just a big steel tube, much easier to paint and far less surface area for corrosion. The latticework is a real pita for maintenance, plus it doesn't take as much rust to compromise a single member of the lattice or a joint/bolt/rivet as it would to actually do any damage to the big honkin' pipes, which might also be concrete-filled.

(disclaimer: I don't know that as fact for ski lifts, but it's true in principle as a engineer)