What kind of question is that? Without knowing anything about the person's geography or local cost of solar, how can you make such a bold assessment of affordability? I live in New Zealand where the capital cost of solar is very expensive and the climate is OK-not-great for solar generation. Even at 30c/kwh the payback (without batteries) is still 15 to 20 years. Not an obvious choice, especially as the capital cost is still declining.
I mean, if you own a house (you cant put solar on the roof of something you don't own), you probably do have access to loans. Houses make great collerateral.
Not neccesarily saying it makes economic sense to get a loan to install solar, just that homeowners usually aren't the poor class that saying usually applies to.
How many people do you know who own a house? Not a mortgage, own.
The housing market is such that a lot of people are overextended, and the mortgage market encourages people to change their definition of 'enough' house which makes it worse again.
The fact that I don't have solar on my roof is substantially my own fault. I moved in a year after a subsidy ended and it contributed to my procrastination. But then my power grid is comparatively cheap and comparatively renewable, which also contributes.
But I know a lot of people who know a lot of people who can't even stay on top of keeping their expected house repairs up. And that's also an investment in energy and your time and having construction people in your personal space for 2x as long as they estimated it would take.