Interactive PDF export bug: Big file size & strange behavior

I exporting a one page document with some photos as interactive PDF and print PDF results in drastically different file sizes (83MB vs 1.7MB) even though the compression, quality and ppi settings are the same. So I played around with the export of the interactive PDF and noticed some strange behaviors I cannot explain: 

1. Reducing the compression, quality and ppi to the bare minimum still results in a very big PDF file size (around 60MB).
2. Having photos embedded instead of linked inside InDesign increases the PDF file size for some reason. 
3. Deleting all the photos from the document only reduces the PDF file to around 40MB, even though there now is only some text visible in the exported PDF. 
4. Only once every single photo is deleted from the InDesign document, the PDF file size gets down to a reasonable 97KB. So simply having photos in the pasteboard actually directly increases the PDF file size! 

The fix is easy: Export as print PDF, works perfectly. But can anyone explain any of the points above? Is there a logic to that or is the interactive PDF export just this broken?

Happing for a few months and over multiple InDesign versions, currently on 21.4. on a MacBook M4 Pro.