Because we are afraid.
Fear of failure: If you are scared that a particular piece of writing isn't going to turn out well, then you may avoid working on it in order to avoid feeling the fear.
Fear of success: Some procrastinators (the author of this handout included) fear that if they start working at their full capacity, they will turn into workaholics. Since we procrastinate compulsively, we assume that we will also write compulsively; we envision ourselves locked in a library carrel, hunched over the computer, barely eating and sleeping and never seeing friends or going out. The procrastinator who fears success may also assume that if they work too hard, they will become mean and cold to the people around them, thus losing their capacity to be friendly and to have fun. Finally, this type of procrastinator may think that if they stop procrastinating, then they will start writing better, which will increase other people's expectations, thus ultimately increasing the amount of pressure they experience.
Fear of losing autonomy: Some people delay writing projects as a way of maintaining their independence. When they receive a writing assignment, they procrastinate as a way of saying, "You can't make me do this. I am my own person." Procrastinating helps them feel more in control of situations (such as college) in which they believe that other people have authority.
Fear of being alone: Other writers procrastinate because they want to feel constantly connected to other people. For instance, you may procrastinate until you are in such a bind that someone has to come and rescue you. Procrastination therefore ensures that other people will be involved in your life. You may also put off writing because you don't want to be alone, and writing is oftentimes a solitary activity. In its worst form, procrastination itself can become a companion, constantly reminding you of all that you have to do.
Fear of attachment: Rather than fearing separation, some people procrastinate in order to create a barrier between themselves and others. They may delay in order to create chaos in their lives, believing that the chaos will keep other people away.
Whether these fears appear in our conscious or subconscious minds, they paralyze us and keep us from taking action, until discomfort and anxiety overwhelms us and forces us to either a) get the piece of writing done or b) give up. (The preceding is a summary of Chapters 2-4 of Jane B. Burka and Lenora M. Yuen's Procrastination: Why You Do It, What to Do About It. Reading, MA: Addison-Wesley Publishing Company, 1983.)
Because we expect ourselves to be perfect.
Procrastination and perfectionism often go hand in hand. Perfectionists tend to procrastinate because they expect so much of themselves, and they are scared about whether or not they can meet those high standards. Perfectionists sometimes think that it is better to give a half-hearted effort and maintain the belief that they could have written a great paper, than to give a full effort and risk writing a mediocre paper. Procrastinating guarantees failure, but it helps perfectionists maintain their belief that they could have excelled if they had tried harder. Another pitfall for perfectionists is that they tend to ignore progress toward a goal. As long as the writing project is incomplete, they feel as though they aren't getting anywhere, rather than recognizing that each paragraph moves them closer to a finished product.
Because we don't like our writing.
You may procrastinate on writing because you don't like to re-read what you have written; you hate writing a first draft and then being forced to evaluate it, in all its imperfection. By procrastinating, you ensure that you don't have time to read over your work, thus avoiding that uncomfortable moment.
Because we're too busy.
Practical concerns: jobs, other classes, etc.
Because it works.
Unfortunately, procrastination helps reinforce itself. When we avoid doing something we dread (like writing) by doing something we enjoy (such as watching TV, hanging out with friends, etc.), we escape the dreaded task. Given such a choice, it's no wonder that many of us choose to procrastinate. When we write a paper at the last minute and still manage to get a good grade, we feel all the more compelled to procrastinate next time around.