An online format can dominate feeds for a week and be embarrassing to use a fortnight later. The collapse is built into the mechanism that produced the rise.
Participation is what spreads a format
A trend spreads because it is easy to copy, and each copy is a new item entering distribution. Growth is therefore driven by imitators rather than by the original.
That produces an accelerating curve, since every successful copy demonstrates the format to a further group of potential participants.
The same property guarantees saturation. A format simple enough to spread quickly is simple enough to exhaust quickly, and the pool of people who have not seen it empties fast.
Novelty is the actual scarce resource
Engagement with a format depends heavily on surprise, and surprise is consumed by exposure. The tenth version of a joke is measurably less compelling than the second.
Ranking systems observe that decline directly, as viewers begin skipping the format faster than they did a week earlier.
Distribution then contracts, which reduces the number of people who see the format, which reduces the number who make one. The decline compounds in exactly the way the rise did.
Commercial adoption marks the late stage
Brands and institutional accounts adopt a format only after it has become legible enough to be safe, which by definition means it is no longer novel.
That arrival is widely read as the end of a trend, and it functions as one, since it signals the format has reached audiences outside the group that started it.
The signaling value of participating disappears at that point, because the format no longer distinguishes anyone who uses it.
Sounds and formats decay at different rates
An audio clip attached to a trend can outlive the specific format, being reused for unrelated material long after the original joke has faded.
Visual formats decay faster because they carry more specific meaning, and reusing them looks like a reference rather than a fresh post.
Platforms sometimes surface older sounds to newer users, which produces small revivals that never reach the original scale.
The cycle has compressed over time
Faster distribution and larger participating audiences mean a format now completes its rise and collapse in a fraction of the time it once took.
Creators respond by moving early and abandoning formats before saturation, which accelerates the cycle further.
What used to be a season is now closer to a week, and the underlying dynamic has not changed at all. Only the speed at which participation saturates an audience is different.