They weren't, that's the problem. Apparently, nurses were putting on as many as 4 pairs of gloves (we typically double-glove for that dangerous stuff), and using surgical tape to close up openings around their necks and so forth. The problem with that is that if any infectious material gets onto the tape, the act of removing the tape can fling that material onto any exposed skin. The hospital did not have the correct PPE available, and nurses complained that their necks were exposed. There have been several news reports about this. I have no doubt that the results of the investigation will be described in a future MMWR issue, so that we can all see what went wrong.
The CDC has stated the nurses were following the guidelines. The CDC guidelines have been inadequate and changing almost daily. You can worship at their altar if you want, but I am disgusted. Not surprised, just disgusted.