Because we and our distributors need to pre-order glass panels from the factory where it is made, on the off chance it will be sold. ONLY 40% of our stock ever gets sold and investment is high. On average each shower contains 2 x rear panels, one left and one right, 2 x side glasses, and 2 x doors. On current ranges and factory demands a minimum order, over one thousand sections need to be stocked just for current models. In addition warehousing room and stocking is expensive over the length of time a panel may be in stock before being sold or thrown away!