All humans by nature are expressive. We express our emotions and feelings through words we speak, through our gestures and movements of body, by acting or writing.
Writing strictly is a form of expression and is restricted to literate people.
That spoken, there are different reasons why people write.
and it is not just limited to expression.
A similar example is acting. Acting is also a form of expression and there are different reasons why people join acting.
I am not talking about professionals here. I am talking about average people like me and you who write.
Expression is one of the reason but that is not lone reason. While this might be responsible for journals, diaries and poetic writing, another reason is collection of memories.
Your role or perceived responsibility might make you write. You feel compelled to raise your voice on certain issues you recognize the importance of. You may build a huge audience and may influence society in a larger way.
You might have gained enough knowledge that you want to share with world. Many people write to educate others.
Writing might be part of your training. Students write day in and out to master the language, solve the problems and so on
It might be just your job to write. Because your writing buys you your gas, you do it again and again.
There would be enough reasons that are not covered here. Help to expand the article.
Just answer why do you write?