Several reasons,I must say-- :for example durability.The TTIV was designed for a tuned pipe which added weight aft of the C/G where as my build is with a 91 FX with stock or custom muffler adding directly to weight of the nose. Second if I do it right .06OZ glass applied thinned,excess soaked up with a paper towel and then givin a second coat of epoxy quickly squeezed off using playing cards or the like leaves you with a sealed and strengthened structure ready for film covering or a couple light coats of paint.
One big reason for not using tissue is concerns of the Nitrate orbutyrate dope dissolving the wing and stab cores..but thats far fetched I know.