Moral outrage does not produce a healthy economy nor does it produce disposable soldiers that you can discard and no one will care.
Living in the real world requires that you acknowledge that sometimes you don't have any good options and have to pick the one that sucks least.
Fighting off the US army attempting to force California to bow to it? Easy. Occupying the US, enacting regime change and a program of cultural indoctrination? Much, much harder.
Oh sure, there'll always be populists who promise that it can be done, that it should be done. They never talk about what it'd cost or if it's even feasible. That's how you get the likes of Maduro, Duterte and Trump with all the entirely foreseeable dumpster fire that results.
You'd think people would wise up eventually.
As for what else have I got? Why, the simplest option of all. Economic victory. The slave states tried to expand their practice and force the North to accept it because they were losing economically as the North developed. Their influence would invariably dwindle to the point where they'd be a junior partner in the state. Some saw the writing on the wall, even if they took the stupid option to try and redress it.
So for California, the more pragmatic option would be to simply make chattel slavery so uneconomical, combined with being completely hostile to any attempts to spread it into California's sphere of influence, that the institution will starve over time even as more blacks flee to less slave friendly territories. How would that development take shape? Largely by developing and competing in the markets that allowed plantation owners to live well. Cotton and other crops. Undercut their product and work out exclusivity contracts so that the slavers simply can't find markets to sell their goods. The long term goal would be to ruin the slave states financially and politically, forcing them to pick between reforming into something more palatable and thus being susceptible to Californian influence (investment and the like), or spend what remains in some futile last gasp spate of violence that'll get rebuffed.
It's a very rough plan, but it's certainly more feasible than the regime change idea. And as an added benefit, is actually more helpful to improving California's economic situation.
Grenada's toppling was made easy due to the fact that the then government came to power in a coup after disputing election results, which made it unpopular to say the least. The embassy rescue is also a low cost investment with strictly defined goals and a very short 'lifespan'.
Contrast instead the occupation of Afghanistan, Iraq and older conflicts where the United States was not seen as a legitimate or benevolent force e.g. Vietnam. A Californian occupation of the rest of the continental US would be very much viewed as illegitimate by the population.
And in all of these cases, America still had access to their vast markets and well developed economies. Economies that simply don't exist in this ISOTed California. There's no external markets to sell to (no one can afford it), no existing globalized supply chains of raw to finished goods. Everything they need to sustain a 21st century economy that wasn't there at the time has to now be developed locally from scratch. I mean things were so bad that you had diabetes patients dying from lack of availability of insulin shots, an otherwise cheap and ubiquitous treatment.
Let us also not forget that armies are expensive, and running them even more so. How many tens of millions of dollars does an expeditionary force consume in a single day of occupation? It's not small. Ergo, California doesn't have anywhere near the economic clout OTL America has to sustain invasions and occupations like in the not-so-old days. On the military side, there's also the fact that California alone has nowhere near the numbers of military personnel to actually run the occupation of the rest of the continent, cut off as they are from every other military installation and force that existed in the time that was. It'd be stretched so thin that Rumsfield's 'lean army' going into Iraq would look to be a tyrannid horde by comparison numberwise. And fixing that means a draft. Guess how well that'd go?
Oh, and it also bears mentioning that this is a California that, like OTL, has experienced two invasions and occupations of foreign states they were told were evil, that they would be uplifting and making better by force of arms. That sentiment sure didn't age very well did it?
As for the 'we'? Who is this 'we'? How about instead I look at you.
Are you willing to give up a significant portion of your income and/or die for this fight? To financially support and stay on the front lines for decades against a restive population who views you as an existential threat to them and their way of life?
Are you?
If the answer to any of that is no, why the hell do you think a vast majority of these other Californians would answer differently?
Moral outrage is easy. Doing something about it and eating the cost? Something else entirely.
