You're forgetting the group of people who want to be readers, but just plain tend to forget that books exist. I keep a big "todo" list on my phone for movies,

You're forgetting the group of people who want to be readers, but just plain tend to forget that books exist. I keep a big "todo" list on my phone for movies, series, and books: every time I come across something which looks interesting, it gets added to the list. But I don't actively take the time to actually purchase anything from it, so it tends to be forgotten. If I were to hear about "Independent Bookstore Day" on a Saturday morning, there's a pretty good chance that would remind me that I have a lot of books to buy, and drop by my local bookstore to buy some. If I happened to be shopping on Amazon and saw a big book sale, I would probably be reminded that I have a lot of books to buy, and see if they were discounted. But if I just purchased a bunch of books from Amazon, I would no longer be going to buy those same books during Independent Bookstore Day, and I would be unlikely to splurge on another pile of books from my local bookstore. In other words, my local bookstore is missing out on sales because of Amazon undercutting them. The trigger isn't "support your local bookstore", the trigger is "books are a thing you can buy".