They're a lot more expensive than fiction as the average text seems to hover around $40-60 CAD in my country, so do they make any money?
Who buys these books?
Who decides if they get reprinted?
Which country buys the most books?
How are the authors paid and what affects demand and how does it affect the academia?
If nobody wants to read, say, a book about Kazakh rituals and ceremonies, does that automatically mean a book like that will never happen since funding becomes nonexistent? How has popular demand affected historical academia?
Who funds these authors if the books don't make any money?
Do they ever make a profit? Who are the most profitable historical writers?
How do Historians feel about people like Dan Carlin who is a "fan of history" but monetizes his podcasts based on his "hobby", and has become a household name when it comes to historical discussion? Meanwhile more credible historians who do not have a popular podcast but write authoritative works on their subjects receive less attention, or remain outside of popular imagination.
Do any "normal" people buy these types of books and how would they find them since they're normally never supplied in regular book shops like Chapters, or are the primary customers just other historians and figures in similar fields?
A monograph such as you named would depend mostly on library sales and sales to specialists. I am more familiar with the UK market but we are often talking about 100s not 1000s of copies. This is also why the default is hardcover. Authors get an advance on royalties and rarely make any real money. In fact, given that years of research and £1000s of grant money go into most monographs, most historians lose money. Production costs for these books are high because the typesetting, proofreading and indexing are very specialised.
Obviously if a publisher has a potentially popular book on their hands they will throw more resources at it and try to get it into more shops.
To really make money from original research, you need a popular subject and a mainstream publisher like Penguin or HarperCollins.
Well publishing is part of a historian's job for which they are paid so it's not totally exploitative. We have to get research into the public domain somehow. You can certainly argue that there are more efficient ways to do it these days and I'd agree - I expect the model to change a lot in the next decade.
Grant money comes from private or state sources. For example the Wellcome Trust is a big funder of medical history. In the UK there is also a state Arts and Humanities Research Council. Historians get money to buy themselves out of teaching and do research. It can be a pretty gruelling process which is one reason I left (my wife still works as an academic).
Funding priorities definitely have an effect on research and there are consequences for academic freedom.
In the UK all research is assessed periodically in an exercise called the REF. University funding and therefore people's jobs are affected so you have to publish books or peer reviewed articles.
On the other side of the argument remember that academics are paid by student fees and taxpayers to research and teach something they love. It's not all bad despite the problems.
When at orientation for my school, one of our professors jokingly said "we've discovered it's kinda nice if our books actually sell" in reference to a few of our professors publishing books that were read by the public rather than just academia.
This was a huge plus for me as I have a bit of a lyrical writing style, as compared to the often cut-and-dry academic histories.
So yes, they are still published by University Presses, but at least the teachers I know have been pushing to be wider read. The best example I know of from my school is Don Doyle's The Cause of All Nations, which has been widely-reviewed by entities other than scholastic journals.
So, yes and no to the normal people question. The professors I'm working with are try to connect with a wider audience, but it's not something mandated or even preferred.