Answer
1. There are a lot more mothers than graduates.
2. Graduates prefer other gifts instead of cards.
Work Step by Step
One possible reason that there are more mothers day cards than graduation cards is that there are a lot more mothers than graduates. As a result, if there are more people who could receive a given card, more of the given card would be written. Secondly, people writ mother's day cards every year in many cases, but not all people write graduation cards for graduates.
