Prohibition of eating legumes on Passover

Rabbi Dr. Avraham the Sixth,
Hello, Rabbi, congratulations and all the best!

Almost 7 years ago, the rabbi published his second column on the site, in which he focused on the flavor of the concern about the presence of chametz in legumes and its halachic validity (https://mikyab.net/posts/732).
However (as the rabbi himself noted), there are several other reasons for the prohibition, such as the similarity between legume dishes and grain dishes (which may lead to confusion between them), as well as the fear that the peoples of the lands will see that legume flour dishes are being cooked and baked on Passover, and will grant themselves permission to bake and cook with grain flour.
Assuming that the rabbi is aware of these reasons, why did he reject them and therefore believe that the prohibition stems from fear (or foolish custom) and not from ordinary custom?

With great appreciation,
A student at the Ponivez Yeshiva.