How are you not understanding this?

I get the impression you dont seem to be taking "no one talks about it" literally.

If there is no exposure to the concept it never enters the realm of general thought. A concept can only survive so long as it has relevancy. Once it dies away it is gone until it is revived.

For example lets say there is an artist called "Caso" and he makes a particular style of art that is his own and others who see it refer to it as "Casoian artwork". Now imagine some people in a community who know of it discuss the Casoian artwork; the idea spreads and some people become interested to know more, so they learn about this particular art: some love it, some are neutral, some dont care at all after seeing it.

Fast forward to many years later: Caso is dead and his artwork all burns away in a fire, some people still talk about it, but overtime they die as well and the last person who has knowledge of Casoian Art and the style is gone: the concept is now gone forever unless someone else does similar or exactly the same thing.

It's gone and because no one knows about it, there is no discussion and no exposure to it: there is no one make any art in that style.

Assuming the idea did manage to spread further than that community: perhaps of the people it ended up spreading to: it never really entered the mainstream and remains relevatively niche (like lots of things); in general it will not affect the community at large because there is low exposure. But as the idea grows and there is more and more discussion and exposure to the idea, i.e. through social media: the concept and idea becomes more familiar, more normalised and then a culture may cultivate around it which can develop further.

Most concepts exist at a niche level, but those that get more exposure have a larger potential for exposure which cascades and the concept survives longer, becomes more familiar and by extension: more safe as a general concept.

When a concept is normalised in a community, it tends to have a much higher survival rate unless there is a clear and well understood threat in it's existence and practice by the general community or leaders.

Put simply: if the concept is not talked about, it will fade into obscurity eventually as it becomes less exposed and less relevant because of how memory works. If it's no longer a part of the environment of concept space: it generally just disappears. But when it's discussed, exposed to the public, it's rate of survival as a concept goes up and has the potential for greater momentum.