Sometimes a press release can make all the difference.
(Sorry can’t find story that old)
Transmeta released two x86 CPUs a bit after 2000, which ended up being technological failures.
Cyrix released some budget CPUs in the 1990s but had legal issues and ran into financial trouble, eventually ending up as part of VIA.
Centaur Technology developed some CPUs in the 2000s, and eventually became VIA's x86 division. They released efficient low-cost processors, which were reasonably successful on the embedded market. VIA is still around, but doesn't bring out a lot of new products.
I think most of them were killed mostly by the dotcom bubble, and CPUs getting increasingly complex. The market just shifted beneath them. It is rarely a matter of just giving up.
In the end Itanium was late and bad project but competition had already folded. Except for amd that had no existing 64 bit cpu and created AMD64 extension to x86. Intel grudlingly got on board but called their clone of AMD64 "IA-32e" architecure in thei marketikg material. The name was later changed to x86-64, only after what I assume when Itanium was internally acknowledged as failure.