Microsoft did port to Itanium. Customers just didn't buy the chips. They were expensive, the supposed speed gains from "smarter compilers" never materialized, a

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.