For example, I use Foxit for looking at PDFs. Maddeningly, I cannot view two PDFs at the same time in different windows. There is no technical reason for this limitation, in fact, the limitation was deliberately programmed into it.

I'm pretty sure the people who program PDF readers have never actually used them. (There are a number of bizarre and trivial limitations to them that are trivially fixed. For example, many readers can only remember the last page read for the most recently read PDF. So if you open another PDF, your earlier place vanishes.)

Another advantage for me of physical books (etc) is that you have something like "tactile memory." What I mean by this is that very often, I can find where something was mentioned basically by how the book feels when its opened (e.g., how thick the pages are in each hand). A similar thing happens with shelves of books.

This is pretty hard to replicate with better tech.

I use a (reasonably good) Android reader which affords metadata presentation and editing, but lacks an "author" field.

Long since reported. Not fixed.

I remember on PDF reader on a tablet which would remember your last read position only in the last 3 PDFs you opened. Open another one, and one gets pushed off the bed. I simply cannot understand the train of thought that concluded that 3 was the lucky number here.