both scythes (and to some extent flails) weren't used for their practicality, they were improvised weapons - they were simply what peasants (usually during uprisings) already had on hand and what could be easily modified by your local blacksmith - scythe was reforged to be straight, making it into some sort of a spear.
concidentally spear would be one of the best, if not THE best, weapon you could give untrained/barely trained peasants.
flails are kinda meh as a weapon, especially in a unit, well lets say spiked flail is a medieval equivalent of spiked baseball bat (it's role, especially in fiction, not as a weapon type)