Because Retics and Hystrix aka "Teacup" rays are only imported by the wholesaler to make money, not for the love of the fish. They are treated, QT'ed, fed, shipped and taken care of completely improperly, and this usually leads to these 'mysterious' deaths.. Which really aren't all that mysterious if you think about it, because most neglected rays will suffer permenant gill or internal damage due to improper handling.. which leads to death down the road.
Another MFK member is having a hard time getting his new inexpensive retics to eat, and you kinda wonder why?
They are treated like any other fish, not a specialty fish Sometimes ignorance can be a 'mystery' to some people..
They are worth the extra money only if you can give them the proper tank space.
I have a little retic and she does fine. Had her for a couple months now and the store had her for about 2 and she is doing great. She is only 5in or so. Retics and histrix are highly underated and if you can find a healthy one go with them.
By the way do you still live in California like it says in your location or did you move to Chicago.