why do the large industrial lathes, 1 HP upwards still use induction motor and not BLDC?
There could be many reasons that they dont want to switch to BLDC motors.


Motor cost: the AC induction motor might cheaper than BLDC motors for their application
Engineering cost: They dont have the expertise or want to develop the expertise to drive BLDC motors. BLDC motors can be complicated to implement depending on what application the motor is being used for.
competition: Why spend all the time and resources converting to BLDC if none of your competitors are doing it. most customers dont care what type of motor that their lathe uses as long as it can do everything(efficiency, noise, weight) just as well as the competing product.
knowing: They dont know that BLDC motors will be better for their application. This is what BLDC motor sales people are looking for.


Everything comes down to where you want to spend your resource(Time, Money) and spending resources on developing a different motor system might be better spend on adding other features to lathes.