Why IBM did not promote PowerPC with Apple or Amiga?
They will be putting much more weight behind it when the next round of consoles will be out, all of them with PowerPC processors (or derivatives).
why IBM did not port AIX OS to AmigaOne
or Pegasos, similar to IBM - BULL agreement?
AIX is not an operating system you would want to run on a desktop, it is a server-side OS developed with big-tin hardware in mind.