Re: Why did they die?
So sad. I would suspect temperature first. It is really easy to overheat the bees in a confined space like a cage. The bees should have had access to fondant if you prepared the cage correctly but water could still have been an issue too. Was this a mated or virgin queen? Assume for a food issue, the attendants would sacrifice themselves for the mated queen. That they all died makes me think something else.
Thankfully, the bees are smarter than I am. They are doing well, in spite of my efforts to help them.