and why the 1930s reference?

I just mean that it's no longer a diphthong for most people, but early 20th-century dictionaries describe it as such. I can't recall hearing it among older speakers, and the other source of old pronunciations is films, newsreels, recordings.

To hear an example you'd have to watch a lot of old film or listen to a lot of old music-hall records on the off chance that someone said ruin, Druid, intuitive, or bruit -- and clearly enough to hear the diphthong.

But I can imagine it: "We're ruined. Do you hear me, Marjorie? Rrruined!"

These days I think they're all disyllables for almost everyone: ru-in, Dru-id, etc.; with how your pronounce the -in -id syllable dependent on your dialect.