Game installations have grown far faster than screen resolutions or visual fidelity would suggest. The causes are mostly decisions about loading speed and distribution rather than raw detail.
Textures dominate the total
The largest share of a modern game's size is texture data. Each surface may carry several maps describing colour, roughness, surface detail and other properties.
Higher output resolutions and closer camera work make low-resolution textures visible, so artists author at high resolution and ship what they authored.
Compression helps but is limited by the need to decompress quickly during play, which rules out the aggressive formats used for still images stored offline.
Data is duplicated to load faster
Reading many small files scattered across storage is slow, particularly on mechanical drives, which were the baseline for years.
Developers respond by packing everything a level needs into one contiguous block, even when the same asset appears in several levels and is therefore stored several times.
The duplication trades disk space for load time, and disk space was historically the cheaper resource, which is why the practice became standard.
Audio is often left uncompressed
Fully voiced games with several language tracks accumulate a large amount of audio, and decompressing it during play costs processor time that competes with everything else.
Storing speech uncompressed avoids that cost but multiplies the space required, particularly when every localisation ships in the same package.
Letting players install only the languages they need reduces this substantially, and the games that offer the option are noticeably smaller on disk.
Patches rarely shrink anything
Updates commonly replace whole packed files rather than editing them in place, because the packing format is not designed for partial modification.
Some systems require enough free space to hold both the old and new versions during installation, which is why a small update can demand a large temporary allowance.
Over a long support period, accumulated patches often leave a game larger than it shipped even when nothing visible has been added.
Streaming assets changes the trade
Fast solid-state storage allows a game to load data as it is needed rather than holding it in memory, which removes some of the reason to duplicate.
Newer engines built around this can be more selective about what sits on disk, though the benefit is often spent on higher detail rather than smaller installations.
Optional high-resolution texture packs are the practical compromise, letting the base installation stay smaller for players who do not need the extra detail.