Expediency while ordering was key with the users we talked to in interviews and observed. Whether they are running to class or need to meet a deadline, users want to be able to order their coffee and exit the cafe in short order. Allowing users to order and pay automatically is simply faster.
Further, the largest reason users cited for avoided using a reusable cup in our survey was a lack of convenience. Enabling a user's cup to pay and order for them directly boosts their convenience, putting them more on par with ordering via a mobile app in advance.