One nice upside to having tex source is that you can set the page size to match e.g., a phone screen. Reading standard pdf textbooks and papers on a phone isn’t very fun.

I used to do this for reading arxiv preprints, but the script I wrote was kind of brittle and it doesn’t really work out with figures anyway

Honestly if the scientific community moved to something that could be interactive and reflowable I would be so happy

Sure, it's easy. But it's hard the other way around.

It's similar to publishing a binary program with or without source code.