The energy required for the first leaves to emerge from the leaf buds of cuttings is stored as carbohydrate at the base of the bud. All that's required for the plant to metabolize that starch and for leaves to appear is water. Once the first leaves open, it takes a vascular connection to roots for the plant to take up the nutrients dissolved in the soil solution, which the plant uses as building blocks in forming the cells and tissues that make up the second generation of leaves. If that connection isn't made before rot prevents it from ever happening, the cutting fails.
One of the reasons it's a good idea to have roots warmer than shoots up to about 72* or so, is that the cooler shoot temperatures suppress shoot growth and help the plant channel energy into root formation. When you are starting cuttings, it's a good idea to do everything you can to prevent rot organisms from fouling the plumbing before the root to shoot connection is made. That is the turning point that determines whether the cutting strikes or fails.
It's difficult to say what might be wrong in either CJ's of DD's case. If the cuttings have roots, there is probably something culturally very wrong. The likely suspects are not enough air or too much water in the root zone, followed by a lack of fertility - more info is needed to make an educated guess.
Al