Because the candy store owner "sizes you up" and believes he/she knows what would suit you best.
So out of the hundreds of possibilities you may only select from the milk-chocolate covered creams. Or maybe only the chewy candies like caramels or the nut brittles. Would you comply with that or would tell the candy store owner to shove it and walk out?
That's kinda like limiting your choice on whom you may hire or choose as your veep. Who is going to stand for that? Kinda wimpy dont'cha think?
