Plus sheer cashflow, not votes, is what's driving a lot of the more water-intensive ag in the dry southern end of the San Joaquin Valley. The Resnicks (Wonderful pomegranate juice/almonds/pistachios, Cutie citrus, billionaire LA residents) are essentially agribusiness investors rather than hands-on farmers, and most emphatically DO NOT have senior water rights for most of their operations, but they DO have the cashflow to buy water off of more senior rights holders, and they have the nationwide distribution on the other end to keep that cashflow going. Whether that continues to be sustainable, or their heirs want to keep it up... we shall see. In the meantime, it is a perfectly reasonable business decision as a senior rights holder to fallow your land or otherwise curtail your use, and sell your allotment down the aqueduct. Fresno State has the California Water Institute which publishes a great deal of informative studies and policy papers: http://www.californiawater.org/publications/ They've noted in the past that transactions like this essentially carry no tax or infrastructure maintenance fees. That's one policy change that could easily be voted into place.
Even setting aside the financial cost considerations other commenters have expressed, getting voters behind a wholesale change is a big project. The water situation simply hasn't started to bite hard enough for the bulk of the state's urban population. I'm often skeptical of ballot initiatives and the necessarily shallow marketing campaigns that accompany them, and a ballot initiative to reform the pre-/post-1914 water rights system would need an absolutely huge, multi-year educational push and likely multiple failures and retries at the ballot box. That's not to say it's impossible, as things are noticeably changing. These days, I live over the hill from Coalinga, which almost ran the hell out of water last year: https://www.cnbc.com/2022/10/24/coalinga-california-faces-th...