I wonder if this is in response to Bookshop.org's DRM free e-book shop. I buy a lot of e-books and have completely switched over because of that feature.
I’m waiting for Bookshop.org to offer an integration with any hardware reader for most of their books. When they do, I’ll switch to whatever that reader is.
It’s up to each author and publisher and the vast majority still use DRM. Science fiction and Fantasy authors (like the example you linked) seem to be most likely to not use DRM, but I don’t read too much of those genres.