In general terms what you really want from CNC machines is to repeat the same actions exactly the same every time, while you may need to monitor and account for things like tool wear, temperature changes, small variations in material properties etc this is still in the realms of fairly straightforward feedback control.
Ultimately lathes aren't the best example as they really only only really have 3 degrees of freedom, cutting speed, tool feed and tool travel. A better example would be 5 or 6 axis milling which is inherently a lot more complex. Here there may well be scope for AI applications, particularly in designing and developing tool path design. This is the process of specifying the sequence of cutting moves to machine a part as quickly and efficiently as possible to a specific quality standard and may require numerous tool changes as well as avoiding collisions, nesting parts, deciding on which order to perform operations, optimising part/billet setup and orientation.
In particular there is a lot to be gained in the paths used for roughing cuts and finding the optimum tool path to move material quickly and effectively for example by taking a smoothed path around sharp corners rather than just using a fixed offset from the final geometry.
Automated tool path design has been around for a while but it is certainly conceivable that AI could have a role to play and it is certainly an important field.