It wasn't because they tasted bad, or at least not only for that reason.  Potatoes are nightshades and are actually poisonous if not harvested properly.  Green potatoes will make you sick or kill you.  Peasants knew what nightshades are and were very suspicious when they were told to eat this obviously poisonous plant.  Bit different when the lords want to keep it for themselves though.  


Also, this trick was done more than once in several countries.  France did the same thing and I've heard of at least one other similar trick.