daniela, Just a question, are you aware that peanuts and peanut products were kosher for Pesach and widely available, and indeed R’ Moshe says that peanuts are NOT kitniyos. I wonder why people “didn’t ask a rav” and decided that peanuts are kitniyos.
While keeping minhag is fine, Pesach also has a “competitive” (for lack of a better word) part to it. There is a thing called Chumra creep and it might not be the best thing in the world. We’ve seen it over the past 50 years with tefillin and kashrus and maybe people want to stop it from getting too much.