PPC being joint design of Apple and Motorola with Apple effectively locking everyone else out of using it on the desktop.
It was
AIM - Apple, IBM and Motorola. Apple at the time was willing to license out their OS for other PPC systems than their own. There was
PREP, there was
CHRP. There were several operating systems targeting the PowerPC, not just IBM's AIX and Apple's MacOS. IBM also had OS/2. Even Microsoft was developing WindowsNT for PowerPC, and there was plans for a
PowerPC 615 with integrated x86 execution to help Microsoft on the way. What pulled the feet under PowerPC on the desktop was Apple pulling their license program, while IBM had already given up on OS/2. Microsoft was more than happy to just stay on x86.
With the ColdFire cutting a lot out of the 68k line, and making it a less than ideal replacement, Apple essentially dealt death blows to the Amiga, The ST and Sharp's X68000 simultaneously.
That is such nonsense - what killed the Amiga, besides Commodore screwing up - was the INTERNET. Networking the Amiga was cumbersome at best, all the software was geared towards BBS and dial-up use. Ethernet solutions were rare and expensive, the TCP stacks (AS-225/Inet-225 and AmiTCP) were not exactly top notch, bug ridden and limited. Not to mention incompatible with each other, and incompatible with Envoy - the networking stack for SOHO Amiga LAN networks. There was zero protection. This was before smart firewalls, even NAT was not common. MuFS was created in sort of desperation. AMIX was there, GNU was there, BSD and Linux came along. A whole lot of Amiga developers moved to BSD and Linux and did well developing on those platforms, most even did it on 68k hardware to begin with - and still do! Porting all this new *ix software to Amiga was sometimes trivial, but most often hard. Fred Fish tried hard. IXemul was born, GeekGadgets, ADE. There was AmiNIX, a BSD kernel running on top of AmigaOS.
But it all boiled down to one single thing - AmigaOS was doomed due to its design, due to one single shared memory space, due to lack of _any_ kind of security. It was obvious that if you put your computer online, you _need_ protection, and Amiga just didn't have that, and hence developers did not see any future in it. Security through obscurity is no good business model.