Demos were once a routine part of releasing a game and are now unusual outside of specific events. Several separate pressures pushed in the same direction.
A demo is a separate product to build
Extracting a slice of a game requires cutting it so it works alone: adjusting progression, removing dependencies, adding an ending, and testing the result independently.
That work competes directly with finishing the game, and it happens at the point in a schedule when time is scarcest.
Teams that once built demos as marketing now spend the same effort on the launch build, particularly since a rough launch is far more damaging than a missing demo.
Distribution no longer requires one
Demos flourished when magazines shipped discs and stores had kiosks, because those were among the few ways to experience a game before buying.
Video changed that. Streams and gameplay footage let a buyer watch hours of a game before purchase, without the publisher building anything.
Refund policies added a second substitute. A short refund window functions as a demo for buyers willing to use it, at no development cost.
Measured effects were not reliably positive
Publishers found that a demo could reduce sales as well as increase them, particularly when the sampled portion was the weakest part of the experience.
Early sections are often the least representative, since they carry tutorials and introduce systems that only become interesting later.
A player who tries that section and declines is harder to recover than one who never formed an opinion, which made the tactic risky.
Storefronts changed what a demo competes with
Digital stores are crowded, and a demo occupies attention that could go to the purchasable product. Some storefronts have handled demo listings inconsistently as a result.
Subscription services provide another substitute, letting a player try a full game at no additional cost within a library they already pay for.
Where trials survive, they are frequently time-limited runs of the full game rather than a purpose-built slice, which costs almost nothing to configure.
Events brought demos back in a narrow form
Seasonal showcase events have revived demos as a promotional device, released for a limited window rather than remaining permanently available.
That framing solves the risk problem: attention concentrates during the event, and a weak reception does not linger on a store page afterward.
Smaller developers benefit most, since a demo remains one of the few ways an unknown game can demonstrate that it plays well rather than merely looks good.