The sentences don't make sense in English as they are written. This may be what the sentences should say: 1. Don't write just for the sake of writing. 2. (see sentence #1 - I think both sentences intend to say the same thing). 3. Don't write essays just for the sake of writing them. In all of these sentences, the meaning is that you should write to achieve some higher goal, not simply just for the writing itself. For example, "Don't write just for the sake of writing, write to improve your grammar for the IELTS test!" I hope this helps.