Because the sacrifice should be shared by all water users, and homeowners are far from the primary consumers of water.
When agriculture uses most of the water, and the most water in agriculture goes to luxury foods like almonds and pistachios, it’s ridiculous to be investigating homeowners while not asking farmers to reduce consumption.
They literally constitutionally cannot ask the farmers, and you need a very mobilized populace to change the constitution. That's only going to happen when people see the consequences of inaction, and its probably better that happen gradually for useless laws then suddenly for all drinking water.
That's not the only way ballot measures and propositions have been passed. Previous governors have advocated for measures, got them on the ballot, and encouraged people to vote for them. The current governor could do the same.
That's because their retail price doesn't reflect the externalities. Cheap subsidized water makes them much cheaper than if the farmers had to pay a fair price.
When agriculture uses most of the water, and the most water in agriculture goes to luxury foods like almonds and pistachios, it’s ridiculous to be investigating homeowners while not asking farmers to reduce consumption.