Its to do with sample rate.
Most tracks these days are 16 bit 44.1 kHz because its what CD's read.
Back in the day before CDs, there was probably little hardware which read off 16 bit (I think, Im not educated about old stuff).
The higher the bit rate, the more complex the sounds are going to be, since theres more information in 16 bit than 8 bit.
THIS MEANS THAT 8 bit sounds like chiptune because the hardware from back in the day wont be able to read high quality sounds, and if it could it would be super compressed and distorted.