Why Ti or Alu? Why not wood?

BOW has been using it for years and if it gets busted then you replace it with another 20p piece of wood rather than £££ for a chunk of Ti. Could use a small electronics box to house all the expensive bits and just have an agreement with other competitors that they don't destroy that bit if it gets torn out. I think the point in the class was that its cheap to repair and easy to destroy, therefore more interesting to watch.