I don't know to be honest. A lot of it has to do with having much muddier, clay banked rivers and warm water which grows a lot of algae which forms a major part of the carps diet supposedly tainting the flesh. I think it is just that people are more used to the less powerful flavour of the white fleshed fish, the ambush hunters with anaerobic muscle for power rather than speed and stamina. A carp has red flesh because of the high amount of hemoglobin in their blood to supply plenty of oxygen to the very active fish.