Legal and liability nightmare I’d guess. Imagine someone dies in a house fire so they sue the repair shop, or insurance refuses to pay because you modified your alarm.
For the same reason you need a licence in most places to install fire and security systems. If you make a mistake, people can die.
The proposed legislation:
https://legiscan.com/CA/text/SB244/id/2832427
(ii) A product or component of an “alarm system” as defined in subdivision © of Section 7590.1 of the Business and Professions Code. Code, including a fire protection system, as defined in the California Fire Code.
I’m guessing because then states would need to heavily modify code laws on things like fire alarm requirements. Those regulations are for anyone who might have to walk into your house.
