I was a HUGE DEC Alpha fanboy at the time (even helped port FreeBSD to DEC Alpha), so I hated Itanium with a passion. I'm sure people like me who were 64-bit MIPS and PA-RISC fanboys and fangrirls also existed, and also lobbied against adoption of itanic where they could.
I remember when amd64 appeared, and it just made so much sense.
That sounds like DEC Alpha to me, yet Alpha didn't take over the world. "Proprietary architecture" is a bad word, not something you want to base your future on. Without the Intel/AMD competition, x86 wouldn't have dominated for all these years.
That's the usual chicken & egg problem... If they sold more units, the prices would have come down. But people weren't buying many, because the prices were high.
Itanium, like Alpha, or any other alternative architecture, would also have trouble and get stuck in that circle. x86-64, being a very inexpensive add-on to x86, managed to avoid that.