The popularity could help feed the popularity...if that makes any sense. For example, usually when there is a refillable mug, we will get one for the family (DH & I will share, or if I'm with my parents we will get one for 3 people). When it is empty, you just go get a refill. But Butterbeer lines are so long, that unless you plan on standing in line for hours, you might as well just get one for each member of the family from the getgo. If a lot of people go from 1-2 "refillable" items to "one for each" it could deplete the supply a lot faster than under "typical" circumstances.