It's all about timing....In autumn and warm spring bees will take down syrup from any type of feeder. In late autumn/ winter/cold spring they won't as the temps are too low. Either they are reluctant to climb away intio a cold feeder ior the tmeps are too cold for them to process the solutioin.
Hence fondant becomes a good food source if required as it's stuck next to them and only requires diluting.
It's worth remembering that bees can only "digest" syrup/honey when it is 50% or less. So honey needs diluting, as does fondant with water before it's of any use to the bees. It's assumed that condensation in the hive can be used by the bees to do this dilution. Notably many early spring flights are for water. Seeley has described them collecting water in Scotland at temps just above 5C.