Like it or not, you have to give people a reason to act. You have to explain "why" your request is worth acting upon.  

• There's 2 different types of "why" - your reason for asking and their reason for acting
• People want to do meaningful work, so that's why you explain your reason for asking
• People also act in their self-interest, so that's why you offer a reason for them to act

The reality - 

• If you ask without a reason, you may have to ask again (and again)
• If you give your reason, you make the work meaningful (which is motivating)
• If you give them a reason, they'll act in their best interest