Blu-Rays don't have DRM that works, you can't make DRM for movies that in unbreakable. You said no DRM. Also some people don't like how low quality the video is on DVDs and only buy Blu-Rays.
I misspoke - I said 'no DRM', when I meant 'no effective DRM'. I don't know anyone who buys BluRays, but I guess there must be some.