Reduce PDF file size after exporting or when exporting from InDesign

To reduce PDFs for preview, i use 

https://www.ilovepdf.com/compress_pdf

Often better results than from Acrobat Pro (file size). Do not use for print things and for interactive forms (makes forms uneditable).

You can only compress things so far, even for vector objects like your illustrator piecharts and graphs, the code needed to describe those objects has a limit. and, in fact, tend remain consistent in size no matter what PDF export ssertting you use. Since compression primarily targets image-based objects, where you have the opportunity to reduce resolution and save with higher compression. None of that affects vector code (unless you have use extendive placed/embedded images in those, of course). In reality, for 120 pages, 82MB is not unreasonable.

Your audit report shows the amount attributed to images, so they don't seem to be the issue. However, Content Streams contain all the ID-native text/objects along with all the postscript/PDF code from the AI files. If you want to source out if a particular placed file be the culprit(s), try make segmented PDFs. e.g save the first half as one PDF, and the remaining pages as another. Compare those sizes. If one is particularly larger than the other, split that one in half, etc etc. This will lead you to pages with "fat" objects on it. Also: if you have some complex graphics as Parent Page items, that could easily add up. But, if all these separate PDFs add up to about 82MB.

Failing all that, try save out as IDML and reopen that. this might chear out some clutter that is complicating in your file.