They had food in frames, not so much but enough.
I think the reason for not taking food was that there were not enough bees of the right age, all bees were busy taking care of larvae. If my theory is right they will take the given sugar solution later.
Usually bees are crazy for sugar, they literally risk their lives for it. In this particular Mini-Plus hive bees seemed to value brood more that what I have seen. Babylovers.