As energy, environmental, or housing policy, it borders on the absurd, as pretty much everyone quickly figured out.
Just to recap, remember that most rooftop solar does not power the house underneath it. The energy goes out to the grid. Why not, you ask? Well, the rooftop energy comes at the wrong time, and we don't yet have economical storage, so you have to be connected to the grid anyway. Given that, the costs of switches to let the roof partially power the house at sometimes, power the grid at other times, is not worth the zero benefit. After all, electricity is electricity and your light bulb does not care where it came from.
So rooftops are just a place to put the electric utility's solar panels. Now let's consider, where is the best place to put solar panels that feed the grid?
(OK, in reality the Mojave desert, or the vast stretches of wasteland along I-5 pockmarked with angry farmer billboards, but the camels are cute.)
Option B: The roof of a typical northern California house:
(OK, I'm having fun with this one, but you get the point. Actually a house off the grid is one place where rooftop solar does make a lot of sense, but you don't have to force people to buy them in that case.)
To belabor the point, people like to build houses near trees. Trees shading roofs are heavily protected in Palo Alto where I live, and you risk massive fines if you cut one down. House roofs don't always pitch to the southwest at the optimum angle.
A house is an expensive and flammable structure for a solar panel. You need to be a lot more careful putting it up there than out in the desert. In California especially, each installation needs a separate design, design review, permits, and so on. Code requirements are stringent. Each installation needs big switches, where the fire department can get at them (and a separate one for the battery). Each house needs a separate set of switches to connect to the grid. All of these fixed costs are spread way out on a commercial solar farm out in the desert.
And so on. We don't operate tiny coal burning generators in each house for the same good reasons.
So why is California doing it? Grumpy free marketers tend to bemoan nitwit liberalism, but economics teaches us to look for rational maximizing actors even in government.
So here is a suggestion. It's actually a brilliant move. Large-scale rooftop solar is only sustained by subsidies -- tax credits for installation and the requirement that homeowners can sell power to their fellow citizens (through the utility) at above-market rates. To put the matter mildly, not everybody thinks these subsidies are a good idea, and moreover you can't count on Washington to maintain subsidies for the 30 year lifespan of solar panels. You never know, someone like, say, Donald Trump might get elected president and start tearing apart energy subsidies.
So, once solar panels are on the rooftops of thousands of registered voters, you have a natural constituency that will vote and otherwise pressure the state, the administration, congress, and agencies to continue solar subsidies.
The Alexander Hamilton story is that he wanted the US federal government to take on the state debts from the revolutionary war, in part to create a class of bondholders who would support the federal government's ability to raise taxes, to pay off that debt. Putting solar panels on houses, though ridiculously inefficient from an energy or environment point of view, achieves the same thing, in a nefarious sort of way.
Too bad they can't just give each of us a solar panel out in the desert, the way some charities show you "your" child in some third-world country. Once a year, you get a card "Happy holidays! I'm your solar panel, number 3457 in the Mojave desert. I've had a great year pumping out electricity! Here is your check for $357.52 in subsidies and power generation. Remember to vote on election day!"