CPTX file size / bloat

This has been an issue for as long as I can remember ... anyone figure out how to shrink a bloated cptx file *without* having to copy out all of the slides to a new project?

I just did the following test: 

[Cp 2019 11.5.1.499 on Win10 64 bit]

File 1 is 505Mb (about 70 slides)

- delete all audio and video and most images from the library

- save file and closed Cp

File 1 is now 200Mb

- Copy all slides and paste in to NEW project --> File 2

- save File 2 and close Cp

File 2 is 5Mb

Clearly Cp is holding onto a lot of stuff even though its library is mostly bare. Anyone have any luck with this?

EDIT: I tried the "fix" here with no luck http://blogs.adobe.com/captivate/2010/10/cptx_file_size.html