It probably took a bunch of lobbying and fighting by dedicated organizations and individuals to get it to go through; Rammed Earth also makes a appearance here.
2016 CalGREEN Code Guidebook
most alternative building codes are covered by a catch-all phrase such as this:
Alternate Materials, Designs and Methods of
Consistent with the Health and Safety Code, and other parts of Title 24,
CALGreen also allows the use of any approved alternate material, appliance,
installation, device, arrangement, design or method of construction
not specifically addressed by the code. The alternates are required
to be evaluated on a case-by-case basis and shall be at least equivalent to
the prescriptive requirements of the code. See Health and Safety Code
Section 17923, and CALGreen Section 101.8 for further details and references.
and usually it means they want to violate your natural design with all sorts of plastic coverings, chemical binders, steel framework, and other terrible gick.
I'd like to see traditional structural cob make the same leap, but that will never happen (likely due to earthquake safety concerns, but more so just crotchety defiance by the Dept of Making You Sad.)