Solar panels are most efficient when sunlight hits them as close to perpendicular as possible. Large scale arrays tend to be 1 axis sun tracking, which yeilds about twenty percent more power with the same panels compared to optimal angle fixed arrays at cost of some small motors, a computer, and incresed space between the panels. Small scale and or rooftop by contrast tends to be space constrained, and often ends up at bad angles.

It still works obviously, but between the fixed angle and cramped space you see significant losses compared to what the same pannel could output in a large scale array.

Cost wise, the most expensive part of any small scale solar array tends to be the labor to install it. Panels are now cheaper per square m than fence posts, inverters are expensive but not that expensive, but design and construction are not. It is a lot faster and easier to have a team start at one end of a field and put down racks in assembly line fashion than having someone come out and design a system, another team climb roofs to install conduit and brackets, then a bunch of electrical work, before finally getting an electrical inspector to come out and sign off on it.

None of this is to say that small scale is useless or you shouldn’t do it if you can, especially in California where Pacific Gas and Energy have spent the last forty years outright refusing to do any maintenance or infrastructure investments unless the govement picks up the entire tab and lets them raise some of the highest rates in the nation, but there definitely is an argument to be made that if the government is paying for it either way than spending should go to the place that gives an extra twenty to thirty percent output for the same cost.