Due to the nature of this kind of data the potential load can be extremely heavy when implemented as an automated report.
For example if you have 100,000 items and 10 locations the this results in checking 1,000,000 records to retrieve the combined levels for the items.
If you then put this on an automated export running every 10 minutes I am sure you can image the potential unwanted load this can have and therefore the impact on your database.
These is the basis for the logic in not adding this to the automated exports
However it is possible to retrieve this data on an Adhoc basis via the following method