One thing to understand is that the "rules" (such as they are) have been influenced by the typewriter, which was the predominant means for creating text from maybe 1900 until computers became pervasive around 1990.
The thing about the typewriter is that it has only one font, and cannot do italics (and can barely do bold). You either use "quotes" or you underline (alas, SE can't underline). So for nearly 100 years the "standards" for producing one-off documents like academic papers (things that did not undergo regular typesetting) omitted any use of italics.
Of course, nobody uses a typewriter anymore, and any halfway reasonable computerized typing setup can easily handle italics, but the academic guidelines in many cases haven't caught up.
So don't expect anything close to an "iron clad" rule here.