The following comment will not apply to all organisations, but with staff and funding cuts all over the show, this may be a contributing factor:
BIM's are publications and should be prepared by various appropriate advisors then passed to a Comms team for formatting, checking and publication. I've recently found that a number of these teams either do not do this work anymore as they are understaffed, or they use software that does not easily give them HTML output.
Joe advisor is left to take care of it and is probably using Word to prepare the BIM and only knows how to "Save as PDF". Or in many cases, print the sucker then rescan it to get a PDF.
BIM's are just the tip of the iceberg. Government Departments are required to produce all sorts of official documents, and more and more back office services are being stripped away, leaving Joe advisor to try and figure out what to do. Of course, Joe doesn't get trained to do these things properly, or get provided with the proper software, so we end up with a growing mountain of paper and inaccessible documents. Google may be fine for some things, but it sure is not a replacement for good process and systems.