Why don't all doctors do hysterectomies robotically?

Many issues. The davinci robot is quite expensive and are not available at all hospitals. Requires a ugeon dedicated to learn the technique and develop experience.
Varies. Not all hospitals have that equipment. Not all physicians are trained for that procedure. Most women would have a better recovery with robotic hysterectomy and it is becoming more common and more available.
Training. There is extensive training needed to do a robotic hysterectomy and not all doctors have done the training. Some hospitals may not have purchased the equipment which is quite expensive.