because oral communications are synchronous, and synchronous communication time is expensive for everyone. It's also important to carefully craft requests sent via email, because your request is probably buried among dozens of other urgent messages. Start by asking for what you need, follow up with a description of the current situation, and then describe what happens if the recipient opts not to supply what you're asking for. If you're not sure what you need, first focus on explaining the problem you want to solve. Then you can work together to first make sure you've found the root problem before you go looking for possible solutions.
Your colleagues and managers are better able to make decisions when they can easily focus their mental energy on what you're really trying to say. Use the inverted pyramid approach to help the recipients of your message get your point.