What? Are you suggesting that aluminium phone cases nowadays are created by an army of trained CNC machinists? And not programmed once by a (few) dozen engineers per model of the handful of existing phone models and then executed by highly automated factories and an army of "low-skilled" workers.
CNC programming isn’t generally performed by engineers—it is currently mostly performed by veteran machine operators.
To get enough veteran machine operators who have the skill and talent to program at the level necessary for high-precision consumer goods, you need quite the workforce pool.
And then add in all the other CNC machinists and manufacturing engineers you need for the auxiliary industries (tooling, molding, the machines themselves) and it starts to add up.
Don’t forget every other industry that is competing for this labor pool.
CNC machines are hard to scale anything more than linearly. We need to train up hundreds of thousands to become CNC machinists. An entire support industry for machine maintenance, tooling manufacturing (an even harder problem), consumable commodities needs to be similarly scaled in parallel.