Why wouldn’t many of them care? The alternative investment for many people with means is the stock market. If I can make my money back on solar in 8 years, that’s roughly comparable to the long-run stock market returns, so it costs me little to sell $30K in stocks, buy a PV system, and feel like I’m doing something concrete to get cleaner energy.

Cut that return to a third of its previous value and I’ll leave my money in stocks and just buy electricity made from natural gas.

Most people don't try and min max every facet of their life. If it eventually returns on their investment relative to dirty energy, they are happy. There's also people who are given the option on their utility bill today to pay extra for renewably sourced energy, and they do it. People put up solar panels in Cleveland where its sunny for 80 days a year, they aren't getting a great ROI but they do it anyhow.

There are non-financial benefits to having solar panels, such as the peace of mind in knowing your home largely runs on clean energy.

Agreed (and acknowledged above). I just think there are more people willing/able to pay a full lifecycle net price of $0 for that peace of mind than are willing/able to pay $20K for it.