Because we rarely have the choice. I'd wager it's a conservative estimate to say 90% of published content is under drm restrictions. I wouldn't be surprised if it was more like 99%.

And what of students with textbooks? Zero choice for alternatives there, and increasingly even the physical versions all come with required drmed additional single-use content making resale value of the book worhtless when once it was a source of a bit of extra money after spending hundreds on them at the start of the semester.