Seymour Dunbar's History of Travel in America

Dunbar's monumental, multi-volume History of Travel in America is only available in snippet view on Google books (e.g. here is volume #3).

But the Internet Archive has these volumes as well

• Volume 1
• Volume 2
• Volume 3
• Volume 4

with downloadable PDFs. Now these volumes are from the University Library of University of Illinois at Urbana-Champagne; but why then does the internet archive also have Google scanned versions of these volumes (apparently from Harvard and Stanford Library), but not on Google books?

• Volume 1
• Volume 2
• Volume 3
• Volume 4

And dont even look at the URL names for the Google book contributed versions ....