Why do some movies with a size of more than ten gigabytes still look grainy and the picture is not very clear?

Current suppression technology generally does not cause problems. Graininess is generally a photography problem when shooting. It may be that the light of the night scene is not strong enough (just like a camera, when the sensitivity is increased when shooting a night scene, noise will appear), or the photographer deliberately created it in order to pursue a certain style or special effect. Of. For example, Kaminsky, a photographer who often collaborates with Spielberg, "Kasnoise noise" has become a term and personal style. For example, "Minority Report" in the DVD era has very strong graininess, which has been reduced in the Blu-ray era. , but still grainy. Even when watching REMUX and Blu-ray original discs, movies like this are still grainy.

Many low- and medium-cost movies often have a grainy feel. I wonder if it has something to do with the equipment used when shooting the movie.

Non-professionals, please answer based on personal understanding, and experts please don’t make fun of me.