While prices have been decreasing, the cost of purchasing and installing solar panels is still too much of a challenge for the average homeowner. And even when government subsidies are available, they are too small to make any real difference. It's true that solar powered systems -- even a smaller system, such as solar water heating -- are capable of providing the energy needs for a home... but the initial investment is daunting, particularly when it takes many years to recoup that investment before you can start drawing energy for free.
It's possible to find used solar panels on the market. The issue is that because it's a relatively new product for homeowners, people don't usually know how to "shop for" solar panels. They don't know what questions to ask or what problems to look for, so for "peace of mind", many would prefer to buy solar panels new. And obviously, new panels cost much more than used ones.
Another issue is the efficiency of solar cells. Currently, maximum efficiency is somewhere around 40% (and increasing, with advances in technology) - but so many factors can affect it, like the amount of sunlight you get, dirty panels, shade from trees or buildings, etc. The lower the efficiency, the more panels you need to generate the amount of energy required for your home. And the more panels you need, the higher the cost.
Finally, another reason why there's a lack of support for solar power comes down to convenience. Simply, electricity is readily available to millions of homes. It's easy to sit back and enjoy this easy and immediately accessible source of power. Solar energy is a "green" alternative and one many homeowners would love to try -- but until technology improves and costs come down, the initial investment cost remains out of reach for the majority of homeowners.