As far as I remember the files in the TI DATs are kept as released zip files, when some publisher released their software to download it contained the full package like screens, manual & other random files.
The ZIP files have been downloaded and not modified, only the filename of the ZIP was renamed, this way all the TI software is the same way it was released, including all files that were in the release.
It is kinda like the first IPF files in the Amiga DATs or the Enterprise DATs, thought there are a lot less "useless" files in those DATs.