Why can't I use writing Task 2 questions that are not on your list?
The main reason is that it ensures we maintain a high-quality service for you. It also allows us to include a sample answer for the question you've answered so that you can compare it with what you've written and better understand your mistakes.
Also, we want to ensure that the questions you're using are reliable so we can ensure that this is happening with our list of questions. It would be ineffective and inefficient to allow students to send us essays answering unreliable questions.