In one of the weekly magazines, I believe it was
Weekend (a gossip rag, so take it with a pinch of salt) there was a theory about the re-appearance of
the collier with the House diamonds. Their theory was that in the last decade of Queen Juliana's kingship (1948-1980), her taste in wearing grand jewels changed.
Until her death (2004), the late Queen Juliana had these jewels in her own possession at
Soestdijk Palace and they only re-surfaced after her death and that of her spouse Prince Bernhard. By that time Queen Beatrix probably regarded herself as already too old for starting to wear such opulent jewels.
When Queen Máxima, known for her love for jewels, got access to these jewels, she decided to make good use of it. It is a theory. Who knows. Fact is that indeed that after the late Queen's death iong not seen pieces surfaced, especially since 2013 (Queen Máxima). I think any guess is as good as it is.