If California would have implemented universal health care for the people in their state then there would never have been this huge fight over obamacare. Same with a host of other issues.
This is absolutely true, but there's a big constitutional stumbling block. Or, more precisely, a big practical stumbling block imposed by a constitutional requirement: the Privileges and Immunities clause of Article IV (not to be confused with the Privileges or Immunities clause of the 14th amendment. Note the conjunction).
Any state that implements its own universal health care must provide the same privilege to all citizens of all states that it provides to its own. It's well-established that this doesn't mean California would have to provide services to people living and being treated in Delaware, and it probably doesn't mean California would have to provide free health care to Delaware residents visiting California, but it absolutely does mean that a Delaware resident who moves to California and becomes a resident of California must be eligible for free health care.
If all states implemented something roughly equivalent that wouldn't matter. But if California did it alone, it would immediately become a magnet for the nation's sick people. There would be an incentive for people to even plan their lives that way: "I'm gonna live where taxes are low while I'm young and healthy and if I ever get a chronic illness or just get to where my medical expenses are rising, I'll move to California". So California's costs would go through the roof since they'd end up footing the bill for much of the rest of the country as well. That wouldn't work.