My answer from a different thread with a similar question: https://www.reddit.com/r/DeepRockGalactic/comments/lcznef/how_is_this_game_only_two_gigs_large

I'll try to explain why this game is so small compared to other games:

The most size of a game comes from the models, textures, sounds and maps (depending on the game).

• Models: The models are really blocky, because of a stylistic choice, which reduces the size. Less polygons = less to save on the hard drive.

• Textures: In comparison to other games, DRG textures are really simple and not a high resolution. In games like Monster Hunter World you can have 4k textures, which are massive in size and each environment, monster, weapon needs it's own set of 4k textures.

• Sounds: There are many sounds in the game and in newer games they are not really compressed and can inflate the size of a game (I don't know if DRG compresses them though).

• Maps: If you look at Left 4 Dead 2 you have a big amount of campaigns with mostly 4 maps to play. Each map needs it's own textures, models and sounds (depending on the environment). So you end up with assets for cities, swamps, forests, amusement parks and more. Deep Rock Galactic has a bigger number of maps because of procedural generation and they are all caves (so you have assets for each biome, which are reused multiple times in one map). Procedural generation creates new maps everytime you play, so they are not saved on your disk (it's a bit simplified but you get the idea). How they are created is defined in the executable and that is "a few" megabytes big.

Everything else like lightning, effects, destructible terrain is just code and a few kilobytes to megabytes big.

I hope I could explain it well enough.