While that is true, one could argue that these reports are either split into distinct parts written by individual authors or are not written in parallel.
A report doesn't have ten people writing the same page. If everyone writes a chapter then merging is trivial. No need to learn a complex tool
For drafting yes, but at some point someone will probably want to edit or review the parts collectively. It's easy to prematurely consolidate the chapters into one file, and then any further changes have to be merged into the 'master'. A proper VCS can help here.
A report doesn't have ten people writing the same page. If everyone writes a chapter then merging is trivial. No need to learn a complex tool