This is very elementary. It is to be one once a year because it is based on the precedent of the passover being done once a year.
You don't need any new testament quotes to know that.
The whole memorial is meaningless to people today, the same as the passover was meaning to generations 100s of years beyond Moses. It was for those ones in the room with Jesus that witnessed his life and death as the passover was for those who witnessed life in Egypt and the passover event.