why is lunch called lunch?

Answer 1

Lunch is a meal that is taken in the early afternoon. The term was derived[1] from "luncheon", which the OED reports from 1580, as a word for a meal that was inserted between more substantial meals, as during the eighteenth century what was originally called "dinner"— a word still sometimes used to mean a noontime meal in the British Isles, and in parts of the United States, Canada and Australia— was moved by stages later in the day and came in the course of the nineteenth century to be eaten at night, replacing the light meal called supper, which was delayed by the upper class to midnight.

Answer 2

Because if it were served earlier it would be called breakfast. If it were later, it would be dinner.

Answer 3

because breakfast and dinner were already taken.