I'm guessing the nominal justification may be 'because fast food workers don't get tips', but the actual reason is in the article. In short, the fast food workers unions were getting somewhere:

Newsom’s signature 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.

[...]

Mary Kay Henry, president of the Service Employees International Union International, said the law capped 10 years of work — including 450 strikes across the state in the past two years.

Would have been better if it was just the minimum wage in general that was raised, of course, but pay rises in one industry will push up pay in others, and hopefully this union victory will help to motivate union efforts in other industries.

It probably will result in it, a rising tide lifts all boats as they say

The new minimum wage for fast food workers will apply to restaurants with at least 60 locations nationwide, with an exception for restaurants that make and sell their own bread, like Panera Bread.