Different situations call for different styles of writing as different situation have different audience. For example, we cannot write a informal letter with a demanding tone to our principle but we can write it in a formal and polite way to request something.
Different situations call for different styles of writing because different situation have a different audience and purpose. To our friends, we can write informally but if we write to people with a higher authority over us, we must write it formally as a form of respect.
The purpose, audience, content and context contribute to the reasons to why different situations call for different styles of writing. For example, we cannot use a very informal and layed back writing style to write to our boss. It would be weird if we would write in a very serious and formal way to a close friend. Thus, in order not to make him/her feel inopportune, we write in the way that the audience would feel most appropriate.
Different situations require different styles of writing as the audience and purpose may be different, hence the tone and registry must accommodate to the situation.
Different situations call for different writing styles as the receiver might be of a higher or lower 'ranking' then you. Why you are writing the email or letter may also require a change in the style.
different situations require different styles of writing as it is a different audience, thus the way you convey your message will differ due to who you are presenting to.
Different Situations have different types of audience, purpose, content and context.