Why are some people so lazy?

How can people do so badly in a class that doesn't require even the slightest effort to get an A or B? In my freshman and sophomore english classes, you never got homework. The only "home work" you had was to read an story out of the book, then the next day you have a quiz on it. He goes over the quizzes in class and you can pretty much cheat, and he wouldn't notice. The bigger assignments you did was write papers, do two speeches, and write journals. You didn't even have to put much effort, and you would get an A or B. But some people couldn't do a speech, or write papers. Why is it so difficult for some people? I don't understand..Why can't some people do the simplest tasks?