Why is it hard to bring a cholesterol level back down?

Sometimes, it is difficult to lower a cholesterol level by dietary means alone (although shifting to a "fishatarian" diet provides more omega-3 fatty acids, and less saturated fats ... and both of these factors do help in the goal of lowering serum cholesterol levels).

It is not so difficult to lower cholesterol levels with drugs, whether using a statin, niacin, bile acid sequestrants, and/or fibrates.