Bigger games are usually 3d games, it is rare to see a 2d game get very large. 3d games are large for several reasons, but here are the big 2:
1- The 3d mesh nowadays can be VERY detailed, it is actually getting ridiculous, we are reaching "triangle smaller than the rendered pixel" kind of ridiculous, so you would need larger space to store them, not to mention that you will need multiple level of detail copies for each object, at least until tessellation become more popular.
2- Textures in 3d is much, much worse than the 2d ones for 2 reasons:
a - In 3d you can get closer and farther away from objects, so the texture on them would need to be much bigger than the screen to not be pixelated, unlike 2d where you rarely need texture bigger than the screen other than the backgrounds, in 3d you need large textures every where.
b - In 3d, textures are not used just for color - called diffuse map -, textures are also used for bump, normal, reflection, refraction, lighting, wet, specular, opacity... and many other types of maps, and almost every object uses multiple of these if not animated ones so the size can get bloated very very easily.
I sill will take mario 64 - 6MB - over
most all of these 30 GB games
. Games used to be fun, not fakely epic, and boring
