Q. Why do we not eat matzah on Erev Pesach?
A second view cites the commandment, “In the evening shall you eat unleavened bread” (Ex. 12:18).
We also need to make a distinction between the voluntary eating of matzah during the year and the obligation to eat it at Seder; an analogy is the rule of not blowing the shofar on Erev Rosh HaShanah, to create a distinction between the custom of hearing it during the preceding month and the obligation to hear it on Rosh HaShanah.