As someone who's worked in the field of used books, I can say from personal experience that's not quite true. It's pretty common to have to type in an ISBN for a variety of reasons. Many times the barcodes have been covered up or defaced, and many publications don't have barcodes in the first place.

It was true, for sure. But the question is, is it still true?

Schools often ask for a specific edition of a classic book and the only way to be reasonably sure you're buying the correct one is to search by ISBN.

Well, just copy and paste from the email you got from school.

I mean, if IT can do anything, it is to solve this problem.

same

ISBNs contain a check digit, to prevent typos. So you’d have to invent a new format.

The point is not just to have universally unique identifiers, but to collect common metadata that's associated with the identifiers. Like this:

https://www.bowker.com/siteassets/files/pdf-files/datasubmis...

Since this is the second time I've mentioned Bowker, let me just say that I do not and have never worked for them or with them, although I did meet with their reps several times when I worked in a different part of digital publishing. It's just that they're inescapable when you're talking about ISBNs.