Worlds and dreamworlds pop into existence all the time, either as a result of deliberately imagining a world (a prime example being popular fantastical works of fiction with millions of fans), through a more direct process, as was done with the Ahona desert or unintentionally. Other worlds have been observed (rarely) to suddenly start existing without any known reason or traceable cause.
For a world to be viable, it needs constant engagement and attention. If interest fades or was never very high in the first place, the world is stuck in the Gyrus and is difficult to get to by dreamwalking. But since information cannot be destroyed, a world will take a very long time to disappear entirely. Yes, information can be overwritten, remixed, corrupted and compressed into near-oblivion, but never destroyed completely.
Past knowledge never fully dies. In some way, it can always be reconstructed and recovered even in every attempt to destroy it. These world fragments, many of which are traces of the past (some claim some to be traces of the future), can remain undisturbed indefinitely. And, as few dreamwalkers get the chance to explore inside the Gyrus, they are likely to stay safe.
Gyrus crumbs are often stranger than their larger and more popular counterparts.
Some of these worlds contain slices of the past. These can be very dangerous. They could entirely wrong, perhaps based on a false memory; they could be changed in subtle ways.
Other Gyrus crumbs are the remains of worlds created by Proseweaver traditions that have since become extinct.
The Id of the Gyrus are few, but dangerous and almost completely unchecked by the Metaparliament or dreamwalkers. The main reason for this is that they usually take the form of entire worlds in the Gyrus (since these are, generally, pretty small and easier to manage and control). These Id may attempt to lure dreamwalkers in. Once a dreamwalker is caught, it is unlikely that they will ever get out as few dreamwalkers even know the Gyrus exists. They are slowly consumed like a fly in a pitcher plant.
Children are the most likely to enter the Gyrus and usually do so by accident. The world crumbs will often fascinate them for what feels like days, months or even years. Unfortunately, children are the primary target of the Id that inhabit the Gyrus. While children are overwhelmingly likely to escape the traps, they are also the most likely to be tempted by them in the first place. Entering an Id-controlled world crumb and escaping is enough to give many kids CHS. World crumbs are also often forgotten myths and stories whose oral traditions (or fanbase) were broken.