[moftz]

It's not an advancement thing, its a cost thing. They made the filter good enough to block out the stuff people can't hear but this device is super loud so you would need additional layers of filtering to completely block it. Smartphone mics need to be tiny so additional analog filtering is going to take up space and resources. You could also run a higher sample rate on the ADC that converts the sound to a digital signal and run a digital filter to cut off the ultrasonic band but that requires more power and chip resources and the ADC might need to be swapped for one capable of the higher sample rate. The tools are all there to defeat this but it's a matter of reducing power, cost, and computing resources.