One of the main causes of death of the new coronavirus seems to be Acute Respiratory Distress Syndrome (ARDS). This can be treated fairly effectively with ventilation, but such treatment would obviously require a bed, ventilation system, and attentive nurses, at the very least. It's easy to imagine how these requirements may currently not be met for all patients with ARDS symptoms in Wuhan.
For more info on ARDS and treatment in the context of the current pandemic, see this informative explanation: https://www.youtube.com/watch?v=okg7uq_HrhQ