I can't speak for why they dropped them, but I can tell you from my own experience due dates were more of a demotivating factor for me. I signed up for the AI class. I diligently went through the classes (and was learning a lot!) however I then had to travel to Japan for work. I went a few weeks where I literally didn't have a minute to spend on the classwork, so I fell behind. Once I missed a due date I lost motivation to continue. :\