I've read a bit about how writing styles may indicate the psychology of the writer. It could be that your stutter has caused you to feel less worthy of being 'heard', perhaps because of feeling ashamed or being taunted for your speech. This might manifest itself in having low self-esteem. And people with low self esteem may write small because they might not feel as if their writing or words are worthy of being read by anyone else. In contrast an extroverted person may write big with grandiose flourishes because they are very confident in themselves and think everyone should read what they have to say. Again, it's just a theory. Your mileage may vary.