IBM did ship a few generations of Itanium hardware, they just smartly never bet the farm on it.

MIPS and SPARC were always a little weak versus contemporaries, if SGI had forestalled a bit with the R18k that would have been enough time to read the tea leaves and jump to Opteron instead.

PA-RISC and Alpha had big enough captive markets and some legs left that got pulled out too soon. That paradoxically might had led to a healthier Sun that went all in on Opteron.