If the R500 requires an oil chang every 13000 miles why does the computer indicate a change needed at 21000 miles?

If the R500 requires an oil chang every 13000 miles why does the computer indicate a change needed at 21000 miles?
They have a sophisticated system inside the ECU that can determine when a service is required depending upon the driving style and journey types of the vehicle. The owners manual or dealership will be able to explain this in more detail.