A lot of that is shadows and lighting data, sometimes in unusual data structures without readily available compression methods. Compressing textures also impacts load times, obviously decompressing 10gb of jpgs could take a while. Still probably there are good compression methods and good tradeoffs to make, if any AAA studios actually cared about storage space (They do care a lot about GPU memory, just not storage space).
A lot of that is shadows and lighting data, sometimes in unusual data structures without readily available compression methods. Compressing textures also impacts load times, obviously decompressing 10gb of jpgs could take a while. Still probably there are good compression methods and good tradeoffs to make, if any AAA studios actually cared about storage space (They do care a lot about GPU memory, just not storage space).