Even the most expensive scopes can fail! You just cannot get quality for 100 dollars! Any one of the components going into a quality scope would cost 100 bucks, by themselves!
Not to mention quality machinery, craftsmanship, and quality control! "Quality Control" helps ensure that you will likely never have a problem with the product! That alone, costs $$$! If you buy Simmons, BSA or Trashco, you are the "quality control!" If it breaks, odds are, you don't send it back! If you do send it back, they take several months before sending you another cheap piece of crap replacement!