Exported PDF file size is 5 times larger than the embeded source files.

Hey everyone,

A quick question, as this still baffles me.

I have a 2-page .ai document (1920x1080, RGB, 72ppi) that includes only two embeded images - one on each page. Both are also 1920x1080, JPEG, sRGB, 72ppi. One is ~600KB and the other is ~400KB so 1mb total.
There is some text on both pages, using 1 font only. No other elements, no gradients, nothing.

Exporting to PDF with default settings (and "Keep Illustrator Editing Capabilities" turned OFF) leads to a whopping 5MB PDF file. If I delete the images and export again, the file is now "only" 500KB (still a lot for 2 pages with text only, if you ask me).
If I use the "Smallest file size" PDF preset, I get a ~530KB file, but with very compromised image quality.
If I use the compress function from within Acrobat on the 5MB file, I get a ~550KB PDF, but with visibly better image quality compared to the Smallest file size preset, but still not close to the original source JPEGs (understanably, since the filesize is now halved).

Why can't Illustrator simply save/export a PDF file, keeping all the source images intact, no recompression/resampling, just embed them in the PDF, so I end up with a ~1-1.5MB PDF? I don't have the original image files, so I can't work with higher quality source files and let Illustrator/Acrobat handle the compression, plus, Photoshop and similar give easier granular control over that anyways.
And by the way, the .ai file, when saved, is 10MB! I honestly have no idea where the extra 9MB even come from, but this seems wrong on so many levels. What if the source images were 100MB and the resulting .ai file was 1GB. How can that be justified? I know that working with linked images is the key here, but I honestly don't understand the logic behind that inflated file size.

PDF files are the de-facto digital document standard nowadays and a lot more are distriubuted as digital-only, compared to those made to be printed somewhere. It looks like this format is stuck in 2005 (which sounds as an understatement, even)