Some games remain actively played a decade or more after release, with content the developers never made. That persistence is almost entirely the work of modding communities.
What modding provides
New content, obviously. Also fixes for bugs the publisher stopped addressing, compatibility with hardware that did not exist at launch, and accessibility options the original lacked.
That last category is genuinely important. Community-made options for colour blindness, remappable controls and difficulty adjustment have made games playable for people the developers did not consider.
The commercial argument
A game with an active modding scene sells for years after release. Titles with strong mod support routinely outsell their own sequels in the long tail.
It also functions as recruitment. A substantial number of professional developers started by modifying a game they liked.
Why treatment varies
Some studios provide tools, documentation and official distribution. Others tolerate it silently. Others issue legal threats, particularly where mods touch multiplayer or reproduce assets from other properties.
The legal position is murky. Mods are usually derivative works, which means they exist at the rights holder’s discretion regardless of how long they have been tolerated.
What breaks it
Anti-cheat systems, which by design prevent modified files from running. That is necessary for competitive multiplayer and frequently applied to single-player modes where it serves no purpose.
Live service architecture is the other obstacle. A game that validates everything server-side leaves nothing for a community to modify.
The pattern worth noticing
The games still being played in fifteen years will be the ones that allowed this. That is a long-term consideration and it competes against short-term control.