The fate of the leading tone accidental - why did they grow out of fashion?

The answer I was given, and it should be cled as a suggestion I suppose, but back then we were taught in a less Socratic fashion. What? Historically Henry the Eighth and Greensleeves being an early example. Is that in the direction of what you were looking for? Early editions(now out of print) Rudiments and theory grades 1-8 sites it and has a good explanation of how and why the melodic minor scale came into existence.