Why are my parents like this?

Your parents just want the best for you. They also want you to accomplish those things they probably did not or could not when they were your age. They are setting you up for the future and believe me it will not be an easy one if you do not have the grades. I probably sound like your parents but honestly they know more than you do. They have a lot more years experience. Remember they're pretty much providing you a home, food, etc. It's their rules you should follow. One thing I do not like is pushing for perfection because there is no such thing as perfect. Be patient, calmly try to explain to them what bothers you, and continue achieving those good marks in school. One day you won't have your parents there and you will miss it. Having parents that care is way better than those that do not or are not around.