It’s the sound chip being weaker on the GBA. If you pay close enough attention, you can tell that more instrument tracks are being played on the snes version. Thus, GBA was ominous while SNES was a banger.
The GBA doesn't have a soundchip as such. It has a stereo DAC (plus the channels from the original GB), but basically everything that comes out of that DAC is done in software, so the number of channels is more or less determined by how much CPU you're willing to devote to sound.
