You'd have a hard time convincing me of that. They had ALREADY tried the Itanium architecture with the i860 and knew that it was horrifically slow for almost all applications.

https://en.wikipedia.org/wiki/Intel_i860

I'd also look at the market of the time. Itanium was in the tech press everywhere. HP-RISC and Alpha were abandoned. MIPS moved into the low-power market. Resources for SPARC and POWER seem to have been cut. Everyone making the top-level decisions was convinced that Itanium and a sufficiently smart compiler were the solution (hint: the halting problem prevents general static analysis as Turing discovered in the 1930s).

Everyone that is, except AMD and Intel. AMD had no alternatives, so they pulled the x64 rabbit out of their hat. Meanwhile, Intel hadn't slowed down their x86 work. When Itanium fell through (like history indicated it would), Intel was out some R&D and some marketing, but had effectively killed off all their RISC competition (it took a decade or more to catch up). Intel then proceeded to Monopolize AMD almost out of existence (and only paid a couple billion in return for their hundreds of billions in profit).

It all works out way too conveniently for Intel.

Itanium supposedly had a "better" 64 bit architecture, but required software creators to incorporate major changes in their design. Also they would have broken backward compatibility with 32 bit software. Since x86 was already popular, the market went along with the extended x86-64 architecture.