I would expect this to be due to low sample rates used by the app. And the source quality is likely not that great to begin with either. It's pretty difficult to have quality sound in the game when many of the games have a poor source to begin with.But overall the quality of the sound is low on TPA. Especially using earpods.. you can tell the quality is rubbish.
But the PC/PS4 versions have HQ sound, so source isn't the problem. It's just that for mobile they have to downsample the BGM/SFX, priority is to keep the app low on storage.