I was wondering why does a hairpiece look good and natural when its wet and looks most of the times bad and unnatural when its dry ?!

i disagree that hair systems look !bad! when there dry youve just answered youre own question,naturaly growing hair looks bad when its dry and to a extent thats what youve got in a hair system minus the natural oils released by the scalp
as dryness is youre biggest enemy wearing.
but hair that dosent have alot of product on it, can look very glossy shinney using the correct shampoo and spray leave in conditioner.

you do have the option of using a vast array of product on youre hair to acheive a wet matt or glossy look, just bear in mind youre aim is to maintain the hairs moisture as it gets no natural moisture anymore from the scalp, oils ect.

anty