Why does every drink need a straw, anyway?
Many of the drinks that would come with such straws are consumed in moving vehicles. In such an environment, sipping from a straw tends to work significantly better than drinking from the rim of a tilted, open-topped cup. While smaller drinks might use a lid with a small gap in it, that just isn't a practical option for larger drinks.
(edited to remove claim that straw is no better than secure lid with a small hole, it could be a little better)