Strength, size and durability are likely the deciding factors favoring the use of SS tubes. An adequately strong pedestal made out of wood could be kind of bulky for the limited space in the average cockpit. The amount of maintenance required might also be of considerartion. Another minor consideration is that most of the accesories that sailors attach to the pedestal come standart with tubing mounts. On a cost basis it would depend on the type of wood used and a good durable wood might be more expensive than SS.