Engineering has the concept of “fail safe”. It literally means that the failure mode is a safe mode. If the dns of the DRM server can no longer be reached, a fail safe would allow the book to continue to be read.
and also, while the iso/tv/movie scene has strict quality rules, the ebook "scene" seems more ad-hoc. pirated ebooks are sometimes OCR scans with tonnes of spelling mistakes or weird formatting, or ancient editions.
in short, de-DRM can still be preferable.