It is likely that the posts are not on concrete footings because the use of treated wood. Even treated they can still rot - just takes longer. IMO wood to earth contact should always be called out no matter where you live. Dry rot in Todd’s hood and moist crud in the midwest.
Items such as stairs that will not be materially affected by frost heave are not required to have deep footings. I have for decades been specifying concrete pads under the ends of the stairs, so that the wood will not contact the earth, and so that a natural point of wear is eliminated.
The former New York state building code had verbiage that supported this practice. It’s too late at night to check the IRC for similar verbiage, but no code official has ever required footings under stair stringers, and I know of no problems arising from this practice.