Why didn't they haul out the big guns? Why should they? Yes, there were people they needed to put into place, and undoubtedly people the NAN shamans needed to train. But for the NAN, well, you don't whip out your biggest gun in response to a threat by the other guy; you pull it just when the other guy thinks he's got the upper hand.
As for the US military putting together their own ritual to disrupt the GGD - this isn't 'hey, we've developed a new weapon' sort of stuff. This is 'there's an entirely new branch of physical law that we've never heard of'. I've never heard of either of your examples, but though yeah, they do sound likely, without major 'ancient' support (such as, I dunno, a Great Dragon founding your hermetic studies university program) it's still a matter of 'one-on-one' work only five or six years after the fact. Sure, I have no doubt that as soon as this stuff went off, every military and law enforcement and spy group in the world had their spotters out for someone who could do that sort of work. And I'm sure they found some people who were willing, whether among their own forces (gotta be some, right?) or someone willing to sign up.
But what you're proposing for the UCAS - major military magical capability and action - is like going from Wright Brothers to an F/A-18 Super Hornet operating off a carrier deck in under a decade. People without tutoring - namely the NAN (who had Aina's kid) and the Aztlaners (who had that corrupted dragon) are at that point still only beginning to learn how to reliably work in concert without blowing themselves up, and that's for the best of them. You're demanding ground-breaking doctoral-level competency from people who've barely gotten through a four-year program, not to mention requiring them to figuratively run out in front of a rampaging tank and try to take it down with a judo throw. It just ain't gonna happen.
As for why the NAN held off, it's because there was a whole shadow war going on. They may not have needed the time to collect and build up a big strike - they could have done that at any time - but it's also a matter of a) getting enough time away from the hunter/killer black ops groups from SEAL Team Six (etc.) and the Rangers and the FBI, etc. etc., b) throwing the hammer they have at a group that maybe is threatening their own people already, and/or c) needing the right time to do it. I mean, you'll notice that the Quad Peak Eruption didn't stop them hunting for him right away; it took those nine months (and three of those in negotiations, presumably with a cease-fire in place) to grind to a halt, still with frequent GGD-driven weather strikes etc. against (generally) military targets.
The NAN took their first psy-ops shot with Redondo Peak - the magical equivalent of a pretty serious FAE. That went off pretty well (so to speak), but it had one or two pretty nasty side-effects - such as the Executive Order, which basically said 'fine, screw you too - we'll shoot every Native American we can find.' And the smaller (per se) GGDances they were using worked just fine screwing with the military operations, they didn't need to go totally bonkers, but they couldn't blow every caravan off the face of the earth. It did, after all, take three years plus for the military to manage to get the pieces into place - this in a world where planning and assembling this should take at most three months, and moving a military group across the country need only take three days at the most.
You can say that the guerilla war was their second psy-ops action, because the US Armed Forces still didn't have a clear threat to deal with. Look at what's happened in Iraq and Afghanistan, then put it in the US West - all of the US West - and add in the fact that there are significant portions of two entire states who have shown themselves to be willing and able to conceal the NAN fighters in their basements and guest rooms, an entire group of people who have a pretty damn good memory about their own persecutions by 'regular' Americans, and who see Native Americans as long-lost brothers. (Literally. For which actions the NAN decides not to kick the LDS Church out - I got the timeline wrong originally.)
Then, when the USA hammer has been finally assembled, the NAN whips out what's the magical equivalent of four multi-megaton-scale nukes and trips the switch - and whether or not he sent an electronic or paper missive, it definitely sends a message of 'look, assholes, we got our kind of nukes too. Do you really wanna come play??' And eventually the threat of that sort of beatdown happening to any city in America (*cough* DC *cough*) is the sort of thing that finally puts the diplomats in Denver, hammering out a peace agreement.
Howling Coyote kept his eye on the strategic plan, and his boiled down to 'smack them hard, keep them reeling, and when they're getting tired but think that you're getting tired and think they've got a chance, hammer them even harder than the first time.' And it worked - in part probably because the military was tired and frustrated with getting into skirmishes in the hills and mountains where they couldn't respond effectively, when they had no ready support, when they could only infrequently manage to locate their enemy; also probably in part because the citizenry was getting tired and afraid of all of it. A year and a half was tough, but the US citizens had still shown the aggression to elect a hawk for President; they would have lynched him if he'd backed down immediately. Another year and a half, and no sign of victory in sight, and then all of a sudden wham - not just one, but four volcanos. Who knows what's next at that point, you know??
A brilliant campaign, brilliantly executed.
EDIT: A couple of things. One, they already knew where the powersite(s) was/were, and it's implied that the Dances happened all at the same site. Second, it's similarly implied that the drain was spread amongst all the dancers, and was not automatically - or even frequently - lethal. (Blood magic may get an additional kick from the actual death, but death isn't necessary if you have a big enough pool to draw from.) Third, pretty much every Native American would have been highly well motivated to volunteer - it's either death in prison, death resisting 'arrest', death on the battlefield, or death dancing. If you can't fight back on the battlefield but you still want to help, and it isn't necessarily going to be lethal (just 'dancing until you collapse from exhaustion'), then ... why not volunteer??
And Mirikon, remember that the Dance was in steady, regular use throughout those three years. The 'weird weather' that frequently disrupted military movements, wrecked bases, or whatnot was Great Ghost Dance action...
