A clip that begins on one service reliably appears on every other one within days, usually without any link back to where it came from. The mechanism is copying rather than sharing.
Platforms are built to keep material inside
Sharing features exist, and they generally produce a link that returns the viewer to the originating service rather than reproducing the video elsewhere.
Since every platform's interest is in retaining attention, none of them make it convenient to move a video into a competitor's feed as native content.
What actually spreads material is therefore outside these features: screen recording, downloading and re-uploading, all of which produce a new independent copy.
Each copy loses information about its origin
A screen recording captures the picture and nothing else, discarding the account name, caption and any metadata that identified the source.
Visible watermarks survive one copy and are commonly cropped out on the next, so attribution degrades quickly through a chain of re-uploads.
By the time a clip is widely circulated, the original creator is frequently unfindable, which is why misattribution is so common with popular material.
Re-uploading is rewarded by the systems receiving it
An account that posts a clip already proven to perform elsewhere is supplying its new platform with material that has demonstrated engagement.
The receiving system has no strong incentive to distinguish original from copied content, since its measurements are of viewer response rather than provenance.
This produces accounts built entirely on redistribution, which accumulate audiences from work they did not make and often cannot be traced to.
Quality degrades measurably with each hop
Every re-upload is a fresh compression of already-compressed material, and the artefacts accumulate rather than being reintroduced from a clean source.
Audio suffers particularly, since re-recording through a device's own playback adds noise and level changes that never wash out.
The recognisable roughness of a heavily circulated clip is therefore a record of how many times it has been copied, not a property of the original.
Why the original often benefits anyway
Widespread circulation drives searches for the source, and viewers who want more from the same creator go looking for them by name or by subject.
That effect depends on the clip carrying something identifiable, which is the practical argument for a visible mark that survives cropping.
Creators who plan for redistribution rather than resisting it tend to recover more from it, since the copying is going to happen whether it is designed for or not.