Back when Randall Munroe released his “What if” in eBook format, it essentially was only available with DRM.
When I emailed him about it, asking for a place to buy it without DRM, he responded with DRM unfortunately being mandated by his publisher, and finished his email with a link to this comic of his:
https://xkcd.com/488/

I have five published books, all without drm. Amazon better not put that shit ON my books. It’s not there for a reason; I want people to share.