Why do I have to fast one hour before Mass?

From an article on Aleteia.org:

Many Catholics from an older generation will remember the “midnight fast.” It meant that one could not eat before Mass starting from the midnight before. For this reason Masses were generally celebrated at dawn and Masses in the evening were extremely rare. Few people wanted to fast all day long before attending Mass and receiving Holy Communion.

This practice of fasting before Mass is an ancient discipline, present as early as the 2nd century. It remained in place until Pope Pius XII reduced the fast to three hours in 1957. The fast was further shortened in 1964 when Pope Paul VI lowered it to one hour before reception of Communion.

The current Code of Canon Law reflects this change and states, “A person who is to receive the Most Holy Eucharist is to abstain for at least one hour before holy communion from any food and drink, except for only water and medicine” (Canon 919 §1).

However, in some cases those rules do not apply. “The elderly, the infirm, and those who care for them can receive the Most Holy Eucharist even if they have eaten something within the preceding hour” (Canon 919 §3).

But why? What does it matter if I ate a cheeseburger right before I walked into church on a day I intend to receive the Holy Eucharist?