R’ Moshe suggests that it’s related to the halachah that one is supposed to involve oneself in hilchos Pesach thirty days before Yom Tov.
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The basic idea is that once the Pesach preparations have begun, one shouldn’t eat matzah until it is obligatory.
The halachah is that that is the day before Pesach, but various minhagim were adopted based on the preparation of learning the halachos, about which there is a machlokes whether that begins two weeks or thirty days before Pesach.