In a way Itanium arguably did pay off, by killing off a lot of RISC competition.

Anyone know why Intel / HP were so quick to productize Itanium?

Given the strong assumptions it was making about compile-time instruction scheduling, I'd have expected them to de-risk the project first. I.e., get a suitable compiler working, and get some benchmark results on a simulator.

There's a good anecdote about that in this fascinating interview with Bob Colwell (https://www.sigmicro.org/media/oralhistories/colwell.pdf):

"Anyway this chip architect guy is standing up in front of this group promising the moon and stars. And I finally put my hand up and said I just could not see how you're proposing to get to those kind of performance levels. And he said well we've got a simulation, and I thought Ah, ok. That shut me up for a little bit, but then something occurred to me and I interrupted him again. I said, wait I am sorry to derail this meeting. But how would you use a simulator if you don't have a compiler? He said, well that's true we don't have a compiler yet, so I hand assembled my simulations. I asked "How did you do thousands of line of code that way?" He said “No, I did 30 lines of code”. Flabbergasted, I said, "You're predicting the entire future of this architecture on 30 lines of hand generated code?" [chuckle], I said it just like that, I did not mean to be insulting but I was just thunderstruck. Andy Grove piped up and said "we are not here right now to reconsider the future of this effort, so let’s move on". I said "Okay, it's your money, if that's what you want." Suddenly this came up again later in another guise but again Andy shut me off, he said "we're not here to discuss it". Gordon Moore is sitting next to me and hasn’t said a word, he looks to all intents and purposes like he's asleep. He's got his eyes closed most of the time, you think okay, the guy's tired, he's old. But no, 20 minutes into this, he suddenly opens his eyes and he points to me and he asks, "did you get ever get an answer to your question?" and I said, "actually no, none that I can understand". Gordon looked around and says, "how are we planning to move ahead with this, if the answers don't make sense?" and this time Andy Grove said to him "We’re not here to discuss that, Gordon"."

It was the next big thing for the government, banks, oil and gas industry, while vendor locking them. It should had bring piles of piles of money.