They dont. I live in socal and have been riding for 10 years and have never seen anything enforced on motos other than noise tickets, if you are ridiculously loud, (streetbikes) and spark arrestors (dirtbikes). Been stopped plenty of times and ticketed sometimes, but never emissions related, ie cats, canisters, or otherwise.
And cali doesnt smog motorcycles. The only exception I know of is if you are re-vinning a moto or bringing a salvaged one back to life (new vin issued). There they will go through the steps of making sure everything is legal, including the presence of cats and canisters, and that is meets noise limits.
One other exception might be for motos that are registered in cali that were not originally manufactured as cali compliant. I have transferred in dirt bikes but emissions dont apply. However I know that this question comes up when transferring in autos from other states, and at the very least the charge an additional tax for it.