Because people still buy them regardless and why spend the extra money? That'd be my guess.

 

Maybe they don't sell as well.

I know I haven't bought a DVD/Blu Ray in a long time, personally. They're feeling more and more like collector things. Not much point loading a release with content if not that many people are buying it.

Then again, AMC is notoriously cheap.

 

Blu Rays in general aren't selling nearly and well and blu ray player sales are tanking. Infact they are predicting now that in probably ten years from now or so physical media will virtually be non existent and they will just release all their products on streaming services.