Sri,
Good question! However, report's SQL related information too is not stored in the system database.
From architectural view, i believe, its not required to store SQL or its related information of each report object on BI Platform keeping in mind the high transactional nature and disk I/O CMS generates. The below reason also holds true.
Reason: If you visualize the information workflow, the query is generated at runtime(actions: viewing or schedule) by the "QT component or QT.dll file" of the report engine in BI Platform.
Hope this clears.
Regards,
Sandeep