I agree.
I don’t think that Amazon went out of their way to specifically not include public domain books - rather, I feel that they were tailoring the list to the interests of most people who read recreationally these days. A lot of classics (e.g. Moby Dick) wouldn’t be appealing to a large part of today’s book-buying audience - they’re too long, or too wordy, or something else that just makes them unappealing to much of today’s reading population. In other words, since “a classic is something everybody wants to have read, but no one wants to read,” (Mark Twain), folks aren’t going to be interested in many of the books which are known to be important books.
Of course, it’s fair to say that Amazon also tailored this list as they did because they want the books on the list to sell. Amazon is a company, and it wouldn’t exist if it didn’t make money.
It should also be noted that just from skimming the list, I saw two public domain books - Great Expectations, and Alice in Wonderland. Both of these books are available free as ebooks from Project Gutenberg, and available as free audiobooks from Librivox yet Amazon still decided to include them. It’s likely that there are more PD books too, which I didn’t notice, but either way, Amazon didn’t completely ignore public domain books. Though I do agree that they are underrepresented.