Generally it's because of lack of knowledge with the owner, some people are quick to use supplements without fully knowing if it's require, some over feed pellets (which are almost all formulated to be fed to all captive parrots, which is a few hundred different species. You can probably see the issue with that...).Are they just pecking at a cuttle fish bone out of boredom? How were they fed it differently/incorrectly?
Essentially it's very possible to leave animals with the option of overdoing something or dying of starvation, so I guess what I am trying to say is just because they are eating something, somtimes you cannot 100% know they actually need that.