To put it poetically, I'm guessing human beings have a strong connection to the objects that hold out beverages. After all, cups are another thing that make us seem less like animals (Instead of just shoving our heads under the sink to drink, let's just do this fancy action in which we just pour the liquid into our mouths with a cylindrical plastic-y object so we seem more civilized than the other animals). Cups +Humans=BestFriend4ever. Without them, we so back down to the level of actual.... ANIMALS!!!
Lol. I love myself sometimes, even if nobody else does :P
'We do not have cups!' exclaimed the young teenage girls trying to perform the Cup Song.