It’s mostly textures, video, and audio.

The game code is probably less than 10gb

Change languages in your game, I am willing to bet it doesn’t download a language pack for whatever language you choose.

You need multiple textures for different screens, resolutions, etc. to provide the best looking results. Multiply by the number of unique environments…

Same with all of the video cutscenes in games, they play pre-rendered videos for cutscenes.