Game installations have grown enormously, to the point where storage capacity is a genuine constraint and download times are a substantial part of the experience.
The reasons are identifiable and several are counterintuitive.
Textures dominate
The single largest contributor. Textures — the images applied to surfaces — account for the majority of the data in most modern games.
Their size scales with the square of resolution. Doubling the linear resolution quadruples the data.
As display resolutions increased, texture resolutions increased correspondingly, and each generation of increase multiplies.
Modern materials also use multiple texture maps per surface — colour, surface detail, roughness, metallic properties, and others — each of which is a separate image. A single material may involve several times the data a simple coloured texture would.
Audio, more than expected
Frequently the second largest component.
Fully voiced dialogue in a large game represents many hours of recorded audio. Multiply by the number of supported languages and it becomes substantial.
Higher quality audio and less aggressive compression add further.
This is why some titles offer language pack selection during installation — the audio for languages you don't use is a meaningful proportion of the total.
Deliberate duplication
The genuinely counterintuitive contributor.
Games sometimes store multiple copies of the same asset in different places on disk. This appears wasteful and was a deliberate optimisation for mechanical hard drives.
On a spinning disk, moving the read head between distant locations is slow. Storing assets needed together in the same physical region, even at the cost of duplication, reduced loading times substantially.
With solid state storage this optimisation is unnecessary, since random access is fast. Games targeting solid state storage exclusively can avoid it, and several titles have reduced their installation size considerably by removing duplication once older storage was no longer supported.
Compression trade-offs
Assets could be stored more compressed, at the cost of processing time to decompress during loading.
The balance depends on whether storage or processing is the constraint. Where storage was expensive and processors were fast, heavier compression made sense. Where downloads were the pain point and drives were large, different choices followed.
Hardware decompression, present in recent console generations, changes this calculation by making decompression nearly free, permitting heavier compression without a loading penalty.
Content volume
Games are simply larger. More environments, more characters, more variation. That growth is real content rather than inefficiency.
There's also less asset reuse. Older games repeated textures and models extensively; higher expectations have reduced the tolerance for visible repetition, which means more unique assets.
Patches and updates
A contributor to the practical experience even where the final size is unchanged.
Patch systems vary in efficiency. Some replace whole files when a small portion changed, meaning a minor fix produces a large download.
Some require temporary space equal to a substantial portion of the installation during patching, which means the effective storage requirement exceeds the stated one.
And repeated patching can leave installations fragmented and larger than a fresh install, which is why reinstalling occasionally recovers space.
What's being done
Selective installation. Choosing language packs, or omitting components like campaign or multiplayer content. More games offer this than people realise.
Better compression with hardware decompression. Reduces size without loading penalty on capable hardware.
Streaming assets. Loading detail on demand rather than storing everything locally. Requires reliable bandwidth and shifts the problem rather than solving it.
Procedural generation. Generating detail algorithmically rather than storing it. Effective for some content types and not a general solution.
Removing duplication. As older storage support is dropped.
Practical management
For anyone dealing with the constraint.
Install language packs selectively where offered.
Check for optional high-resolution texture packs, which are frequently separate and account for a large share of the size. On a display where the difference isn't visible, they're pure cost.
Reinstall occasionally rather than patching indefinitely, which can recover substantial space.
And storage is cheap relative to the time cost of managing it. Adding a drive is frequently the more sensible response than repeatedly uninstalling and redownloading, given that downloads consume both time and bandwidth allowances.
The bandwidth dimension
An aspect that affects some people far more than others and rarely appears in discussion.
Large downloads assume fast, unmetered connections. For anyone on a capped plan, a satellite connection, or in an area with limited infrastructure, a hundred-gigabyte download is a substantial imposition rather than an inconvenience.
Physical media has largely disappeared for this reason and others, and where discs are still sold they frequently contain a fraction of the game with the remainder downloaded.
Which effectively excludes people whose connectivity cannot support it, and it is a form of access barrier that gets little attention in a discussion dominated by people with good broadband.
Worth adding that storage speed now matters as much as capacity for some titles. Games designed around fast storage assume assets can be loaded on demand rather than held in memory, and running them from slower drives produces stuttering that no amount of processing power resolves.
Which means the storage decision has become a performance decision rather than only a capacity one, and it is worth checking a game's stated requirements rather than assuming any drive will do.