Because they can!
Why is a guitar made of wood?
Because its counterproductive to use silk as a building material for the body
Why do spiders have 8 legs?
Kigurumi (F) yellow PK 7/4/13, Kurama VT 9/8/13, Zeydalus Salamander EE PK 21/3/14, Ryuk turquoise dragon DeT 8/5/14----Crested Gecko (8ths old) Sven Cal 27/12/11,
RIP: Osiris copper DT, Nel blue VT, Nelliel turquoise grizzle DT, Zaku red cambo, Blitzkreig Pineapple CT, Halloween orange chocolate DeT, Grimmjow, turquoise green CT