First, I have an ambition to master English to make my dreams come true. I believe that writing helps to improve my English. That's the main reason for me to keep on writing in English. I know everyone has the similar goal in their another language, but while keeping a diary, majority of people can't maintain their motivation and they stop it.
Second, I know myself very well. Once I become lazy, it's hard for me to go back. That's the second reason for me to keep it up.
Writing is already a part of my life and it's not difficult for me. I can express what I want to say in English but I still can't express anything in a natural way. That's the problem for me now. When I started writing, my goal was to keep writing every day, but now my goals is writing natural English.