The main reason for this is that if we included the data of single files, the exported XML files would grow considerably and reach a size that cannot be handled reasonably.
Other export types, like Excel or PDF for example, allow including single files if it has been configured like this in the settings.
Since v9.0 you can also export the whole scan, including single files to an SQLite file. These database files can be reimported and worked with in TreeSize, just as you already know it from the XML files.
In case you need data like history data or growth reports on file level, we would like to recommend our product SpaceObServer. It regularly collects the file system information using a background agent and stores it in an SQL database, including size development and (optionally) all permissions. The reporting is faster and more flexible compared to TreeSize, because it is built on a database and collects data on file level. SpaceObServer offers advanced scripting capabilities through OLE Automation.