On the picture below you can see that behind the frame there is something extra to balance the diadem. Especially worn in full setting, with the middle prong (not worn here), the diadem seems to be top heavy. There are pictures of Queen Beatrix on a State Visit in Portugal correcting this diadem because it apparently felt like toppling from her head. Maybe that is the reason Queen Beatrix always tilted it so far backwards and wore the sides hidden in the hairdo.
The new frame looks like balancing the diadem somewhat better and also looks like taking away some weight from the actual frame itself.