CNC machines are not always efficiently used when programs are modified by hand on the machines...
Manually programming CNC machines is very expensive...
80 % of programs contain errors mostly caused by accidental incorrect entries
In 70% of milling jobs only 2 axes are used, so why use a complex system if you almost never need it for your simple parts?
30% of the time CNC machines are used for simulating and testing purposes...
To have a CNC machine not actually producing anything is very expensive especially when simple work pieces are required.
Training of your staff enabling them to use complicated CAM software can be a problem... It costs time and money.
Manually re-entering a list of drill co-ordinates is often fraught with errors.
Finally your CNC machines are less cost-effective as they could be !