As a kid (1950) I was taught that quotation marks were used ONLY in quotations and magazine articles, etc., and that book titles were to be ALL in capital letters or underlined. (Upon reflection, the nuns did teach me a lot of stuff that wasn't true)
Typewriters did not have italics. They had an underscore key but it was cumbersome to backspace all through a title to underscore it, so CAPS were the easiest and quickest way to go. In written work in school, CAPS were also preferred being neater than hand underlining without a ruler....
DU's format doesn't allow formatting of thread titles other than quotation marks which I feel aren't quite right in a book titles. Emails don't have formatting options in the subject line.
When the computer came along, somebody decided that all CAPS was
screaming probably because there were so few people using computers that they wanted to get their monies worth

out of the italics and underscore keys. I personally don't like to read things printed in italics and dread reading more than a paragraph (I wonder if this is because italics in fiction are the crazy killer thinking).
College and University websites now all seem to approve of book titles with the first letter of words capped in combination with quotation marks. I feel uncomfortable with that because it's in direct opposition to what I was taught.
So bear with me and my book titles all in CAPS. Honest, I'm not screaming at you, and will use them until our Hosts tell me to stop...
The list that I typed in another thread took ages to look up and even longer to type and I'm putting this separate so that the list could be neat and and easy to read and use with none of my bs....