Of course it is possible.
The processing power is there in the phone.
There are a number of plugins or hardware solutions available for studio work. Examples include Waves NX, Toneboosters Isone, Sonarworks Reference 4, 112dB Redline monitor and probably many more. As far as I know they are not super popular, but what do I know. I do not know if they are ...
"I'm asking why this isn't already done."
Because it is not necessary.
Why mess up a good stereo recording.
Another reason; the music should be played the way it was recorded and NOT bastardized by some "smartphone" algorithm. If it is recorded in Stereo, play it in Stereo,If it is recorded in Binaural, play it in Binaural.
But that's ...