That's not at all what happened. Intel's 64-bit story was EPIC/IA-64/Itanium and it was an attempt to gain monopoly and keep x86 for the low-end. AMD64 and Itanic derailed that idea so completely that Intel was forced by Microsoft to adopt the AMD64 ISA. Microsoft refused to port to yet-another incompatible ISA.
Had Itanium been a success then Intel would have crushed the competition (however it did succeed in killing Alpha, SPARC, and workstation MIPS).
I don’t think it was Itanium that killed SPARC. On workstations it was improved reliability of Windows and to some extent Linux. Sun tried to combat this with lower cost systems like the Ultra 5, Ultra 10, and Blade 100. Sun fanatics dismissed these systems because they were to PC like. PC fanatics saw them as overpriced and unfamiliar. With academic pricing, a $3500 Ultra 10 with 512 MB of RAM and an awful IDE drive ran circles around a $10000 HP C180 with 128 MB of RAM and an OK SCSI drive because the Sun never had to hit swap. I think Dell and HP x86 PC workstations with similar specs as the Ultra 10 were a bit cheaper.
On servers, 32 bit x86 was doing wonders for small workloads. AMD64 quickly chipped away at the places where 1-4 processor SPARC would have previously been used.
I think that Itanium had zero impact on anything (besides draining Intel for money) due to high cost and low performance.
It could not run x86 apps faster than x86 cpus, so it didn't compete in the MS Windows world. Itanium was a headache for compiler writers as it was very difficult to optimize for, so it was difficult to get good performance out of Itanium and difficult to emulate x86.
Itanium was introduced after the dot-com crash, so the marked was flooded with cheap slightly used SPARC systems, putting even more pressure on price.
This is unlike when Apple introduced Macs with PowerPC cpus: they had much higher performance than the 68040 cpu they replaced. PowerPC was price competetive and easy to write optimizing compilers for.
Itanium itself did nothing. But Itanium announcement killed basically killed MIPS, Alpha and PA-RISC. Why invest money into MIPS and Alpha when Intanium is gone come out and destroy everything with its superior performance.
So ironically announcing Itanium was genius, but then they should have just canceled it.
Microsoft did port to Itanium. Customers just didn't buy the chips. They were expensive, the supposed speed gains from "smarter compilers" never materialized, and their support for x86 emulation was dog slow (both hardware and later software).
No one wanted Itanium. It was another political project designed to take the wind out of HP and Sun's sails, with the bonus that it would cut off access to AMD.
Meanwhile AMD released AMD64 (aka x86-64) and customers started buying it in droves. Eventually Intel was forced to admit defeat and adopt AMD64. That was possible because of the long-standing cross-licensing agreement between the two companies that gave AMD rights to x86 way back when nearly all CPUs had to have "second source" vendors. FWIW Intel felt butt-hurt at the time, thinking the chips AMD had to offer (like I/O controllers) weren't nearly as valuable as Intel's CPUs. But a few decades later the agreement ended up doing well for Intel. At one point Intel made some noise about suing AMD for something or another (AVX?) but someone in their legal department quickly got rid of whoever proposed nonsense like that because all current Intel 64-bit CPUs rely on the AMD license.
Maybe I wasn’t clear; I meant after Itanium failed, Microsoft refused to support yet another 64-bit extention of x86 as they already had AMD64/x64 (and IA-64 obviously)
Had Itanium been a success then Intel would have crushed the competition (however it did succeed in killing Alpha, SPARC, and workstation MIPS).