They’re not really "different", but include for instance more or different instruments. I’d say it’s for people that want to hear something different. Also do take into account that it’s a GBA score so overall "quality" compared to the SNES score is… lower I’d say.
(SNES Sampling rate > GBA one). Otherwise it’s a refreshing listen :3
Also, IV has seen the least work. I can’t vouch for V as I never played the SNES version (!), but VI seems to be the one which has seen more work.