> I'm curious did Itanium fail because the model of pushing the complexity onto the software and a human failed or did it fail because of lack backward compatibility for a world that was largely x86 at that point?

It's closer to the truth to say that Itanium caused the world to become largely x86. In the 90s, while the personal computing market may have been dominated by x86, the workstation and server markets (which was the segment Itanium was targeting) was definitely a lot broader and competitive. HP canceled its own architecture line to focus on Itanium, and a couple of other architectures saw roadmaps dwindle because of it.