From my experience, the issue in the US is on the demand side. People here hardly read, and when they do read, it’s usually a super popular book all their friends have read or that Tim Ferris talked about. When I published my book, I was surprised by how many close friends and family bought the book to support me, but have never opened it. And it wasn’t until after I published my book and became more aware of the reading habits of those around me that I realized how little most people read these days. There are a handful of people who read 30-50 books, but if you were to take the median so those people don’t skew the average, I’d estimate that it’d come in around 1-2 books. Probably half of the people in my life don’t read a single book in an average year.
While I never wanted to make a living off my book, I’ll admit it was discouraging to see how few people read it cover to cover. I took Mark Dawson’s course and got all of the social ads, lead magnet, etc. setup. The ads did work, but I quickly found out that of the subset of people who do read a lot in the US, most are 60+ and want self-published books to be either $0.99 or free. I had multiple angry old ladies reach out to me through my Facebook ad complaining that they weren’t going to pay $2.99 for a self-published book and that it was upsetting I’d even try.
It wasn’t all bad and I did find readers who genuinely enjoyed my book and supporting self-published authors, but these type of people are a very small percent of the population. If the average person read 15 books per year and was ok paying $10 per book to support authors, I think you’d see a lot more self-published books. From my anecdotal experience, there are plenty of people who aspire to write, but we lack a supportive reading culture to fully cultivate authors (even part-time authors).
EDIT: I’ll also add that among the people in the median reading 1-2 books per year, most are listening to those books as audiobooks. I’m not one of those people who say listening to books isn’t reading, but for the average full length novel it costs about $10k to get an audiobook made, which is way outside the budget for anyone trying to publish books as a hobby. I paid for an audiobook to be made because I have the income and thought it’d be a fun experience (which it was!), but I will never make enough from the book to cover that expense