ISAs fail to gain traction when the sufficiently smart compilers don't eventuate.

The x86-64 is a dog's breakfast of features. But due to its widespread use, compiler writers make the effort to create compilers that optimize for its quirks.

Itanium hardware designers were expecting the compiler writers to cater for its unique design. Intel is a semi company. As good as some of their compilers are, internally they invested more in their biggest seller and the Itanium never got the level of support that was anticipated at the outset.