The architecture was probably a fatal mistake on its own (even if Intel had disbanded its x86 line, the “older” RISC processors outperformed, often substantially) but ensuring that almost nobody saw anything close to what performance it could deliver definitely made it fatal. If Intel hadn’t been greedy trying to charge for compilers, the gap wouldn’t have been nearly as bad.
This must have been a huge part. Maybe ICC could squeeze more MIPS per dollar out of Itanium than x86, but if GCC can't, people are going to not buy Itanium rather than buy ICC.
I think that's the kind of issue they're talking about. If it had been easier for nerds in bedrooms to run Itanium, we'd've seen much better support for it in GCC etc. much sooner.
Back when I supported computational scientists, the total cost of the servers + compilers was so steep that even if everything had worked as well as the Itanium salespeople promised it would have needed to be many times faster to be worth the hassle of changing toolchains, especially since you had to pay up front for the hope that with a fair amount of work you'd at least hit the point of breaking even.
If Itanic had won, we'd still be basically where we are today from a hardware perspective, but with even less competition.
I think the lack of availability certainly didn't help, but the architecture itself was probably the biggest downfall of the IA-64 platform. When it was introduced, the hardware was certainly advanced, but relied too much on software to get proper performance out of the chips. The product was doomed from the start.
Ampere will likely have entirely different problems bringing their architecture into the market, but I don't think Itanium ever stood a chance even if they'd sent out free chips to as many influential people and companies as possible.