I bet you find that the reason they never made it to the Amiga were economic ones.
- Licensing issues (another company had the rights to the Amiga version)
- Sales. Perhaps the ST sales sucked so they didnt want to pay for the conversion or the money to promote the conversion
- Memory, several ST programmers complained that what they could do with 512k on the ST, they needed 1Meg on the Amiga, at the time 512k upgrade cost a fortune.
just my opinion