Has there been a surge, or were previously such things suppressed? Also, most books are marketed via publishers which means there is filter (read: bias) in what

Has there been a surge, or were previously such things suppressed? Also, most books are marketed via publishers which means there is filter (read: bias) in what gets published and what does not. It's an interesting idea (i.e., analyze books) but the context is going to influence the results.