Does anyone exactly know why munggo is served mostly during Fridays?

I was watching a local noontime television show one time and the hosts were making jokes out of their lunch. It was Friday and their lunch was "ginisang munggo". I honestly have no idea too why it is mostly served during Fridays. My mom mentioned that it is because of the lenten season. Traditional Filipinos adapted the lenten rule that you cannot eat meat during Fridays. However, some of my titas say that they cook munggo every Fridays because it lasts until the end of the week even without preserving it.