According to a commenter in one of the past topics made about this, it's possible it is/was an experiment in regards to the Mandela effect and whether it can be weaponized in some way. Disinformation, altering public perception, actively changing recorded history in small, but directed ways for the purpose of discrediting or whitewashing historical figures, attacking activism talking points or destroying protester credibility.

The cornucopia was supposedly used because enough time has passed since its production period and most fabrics have naturally degraded by now. Any remaining samples can be considered as knock offs, deliberately made now or even ai hallucinations (Wait, this was before ai lies became a thing). It is a small and common symbol many have seen, yet paid little attention to because it was small and common. So many tiny details in life, how can we remember them all correctly? And that's how it supposedly works. Take a detail we take for granted and can be changed, then remove or switch it to imply something else.

But here's the rub. People do wrongly attribute historical details to the wrong people simply because it's popular. An example being the "Let them eat cake" quote, wrongly attributed to Marie Antoinette, yet actually being a disparaging remark made by some random revolutionary author who really didn't like her.

So even though someone proved the cornucopia existed and was forgotten again and again, the conspiracy remains just a theory. Because it's silly and simpler to believe there was no cornucopia in the first place.

Even if there is a conspiracy, it's a silly one as you say. It seems like a lot of work for nothing, with large chances it would fail. And yet, its theoretical purpose has far-reaching connotations. When we can no longer trust our own memories or even the small proofs we find, those who control our knowledge can shape it to fit their purposes at leisure.