The music industry situation was different. At the time the market went to drm-free by a landside, music playback devices by and large had no wireless or cellular radios. They were fixed-function devices that could only consume non-executable content (mostly). In that ecosystem, supporting multiple platforms was difficult to the point of being unfeasible. For the no-name cheap devices, DRM was completely out of reach. Customers more keenly felt the pitfalls of DRM given the state of the ecosystem. Even if each publisher *could* put their content into walled garden apps, the nature of how music is consumed suggests back to back playback of arbitrary selections from a customers library over the course of minutes. Also, ripping CDs was trivial for even casual users.
The state of devices used for reading and movie playback are generally internet connected and companies can deploy their own content management application. Having to navigate and switch between the applications is less disruptive relative to how much time the consumer is going to spend in one specific work. Scanning books in is in no way feasible as a casual endeavor comparing with CD ripping. All the 'no name' devices that are available are android devices meaning DRM is feasible.
I'd like to think that the music industry went mostly DRM-free because they saw it as the non-evil way to go, but it was more about feasibility and the CD market pretty much leaving the barn door open, rendering it a silly exercise to DRM protect content that is trivial to rip in other ways.