From the article, it sounds like there’s been specific legal stuff going on that influenced this:

Newsom’s signature on Thursday reflects the power and influence of labor unions in the nation’s most populous state, which have worked to organize fast food workers in an attempt to improve their wages and working conditions.

It also settles — for now, at least — a fight between labor and business groups over how to regulate the industry. In exchange for higher pay, labor unions have dropped their attempt to make fast food corporations liable for the misdeeds of their independent franchise operators in California, an action that could have upended the business model on which the industry is based. The industry, meanwhile, has agreed to pull a referendum related to worker wages off the 2024 ballot.

So yeah, labor unions bringing cases that could effectively dismantle the corporate/franchisee relationship is a big, big deal to fast food companies, which are generally the most “franchised” types of businesses in the US. Agreeing to higher pay to slow unionization efforts and to outright stop cases that change how the core of their businesses function seems like a smart short-term move on their part.

It would still be better if it was for everyone, but this particularly seems to have some history behind why it happened for just these workers.