I agree most people don’t realize that film can look “hd”, though it’s not really their fault, they’re just not aware of it (I wasn’t too until some years ago! 😄 ).
About grain, though, I don’t know anyone who actually dislike it. Maybe they use DNR on movies just because it eases digital compressions and makes special effects blend better with the live-action footage.
Ease of compression and vfx blending have little to do with it.
They use DNR because they think that’s how people want their movies to look.
At least they’ve rectified many of the more egregious examples with proper remasters.