Business models like self-publishing and Kindle Unlimited have worked really well for romance and fantasy novelists who can publish six books a year and have fans who plough through two books a week. They absolutely have not worked for literary novelists, let alone historians, biographers etc. If the "sell copies of books to readers" model dies, it will change the kinds of books that get written. For people who see books as a fungible commodity – any book is about as good as any other – that's fine. For the rest of us, it isn't.

You make an assumption that people aren’t willing to pay to support the creation of non-fiction books. I think this is bunk.

An extremely relevant example: Veritasium. He creates well researched and scientific videos on YouTube (at a rate of maybe 3-4 a year), and has almost 5,000 patrons.

Again, can every author survive this way? No, but there are other options; please don’t get hung up on the familiar and call it the only way.

What are your options if your book is going to take years of work and you don't already have a following?

All of the authors I currently follow did exactly this. Word of mouth, some basic marketing, utilizing their contacts and their followers. The internet doesn't only support zeitgeists, they also support niche communities which spring up out of nowhere.

Start with something smaller or find an interested wealthy patron. Same options as if I wanted to start a business that will take years of development to achieve traction.

How does anyone get a following? You build it over time.

I can assure you there are a lot of great books that would not have been written if the authors first had to either 1. become beloved enough on the internet that they could crowdfund their income for five years or 2. somehow secure a "wealthy patron" who wanted to finance it (I can imagine a pretty fierce competition for that pretty rare beast).

How does copyright help with that scenario?