Joseph: I think that the logic is that the mitzvah of maztah and the requirement to koveah seudah on it instead of chametz gives it a higher status as bread and therefore befitting a hamotzi.
The creation of minhagim is based on logic, it’s only the abolishment of a minhag which cannot be done using logic since once a minhag is established it becomes part of halachah (depending on the level and widespread acceptance of the minhag) like a takanas chazal and must be followed irregardless of whether the reason still applies.