In New England & NYC, a 4-way stop is usually used for urban neighborhoods where single-lane, low-traffic streets meet. Roundabouts and slip lanes are space-prohibitive in these situations (they'd have to go through privately-owned lots), traffic lights are overkill given the light traffic, and visibility is insufficient for a safe 2-way stop or yield.
In CA and other western states, these same neighborhoods are usually suburban houses with lawns, and even the apartment buildings have setbacks from the street. A yield would work fine, but either for habit or consistency, it's signed as a 4-way stop. Drivers feel like they have good visibility and it should be a yield, though, and so they roll through it.
It probably depends on where in CA. Have been living in Bay Area, mid-Peninsula, for 18 years and i've so far seen most people (and myself included) do complete stops. And just recently saw police stopped and cited a cyclist for the "California Roll" in Los Altos.
[1] https://www.urbandictionary.com/define.php?term=california%2...
This definitely varies based on where in the US you are. In California almost no one comes to a complete stop. (That's probably why rolling through a stop sign is called a "California Roll"). But in many other parts of the country people do, even if there are no cars around.