I was reading the comments in YouTube, not quite as unsatisfying as you might imagine, and a light bulb went on for me. In my youth tenors sounded like Placido Domingo and Franco Corelli and men were admired for their macho behavior. These things actually go together. Wagner, late Verdi and Puccini were the models for sound in all voice types.
Then along came Maria Callas singing operas from the earlier bel canto period but in a somewhat heavier technique. In those days Norma was the hardest popular role to cast.
In eastern Europe, Russia, Romania, etc., these heavy techniques continue to mark the standard for operatic training for both men and women. But for the rest of us our tenors are of a lighter model. We should remember the article in the New York Times in 2014 about New Three Tenors: Camarena, Brownlee and Florez. These three tenors, all from the western hemisphere, are all leggiero tenors, tenors with lighter, less legato techniques, and are best suited for the music of Rossini and Donizetti.
What else has changed during this period? We have lived through the women's movement. Another thing that has happened over the same period is the rise in popularity of the countertenor, a voice that sounds mostly but not entirely like a woman.
So there it is. Life has changed. There are more women in congress than ever before, women occasionally conduct symphonies, and unwavering masculinity is no longer a standard for men. They might be gay. They might be countertenors.
I confess that I have not seen this correlation before. I cannot explain why. But it follows the concept that changes in life are reflected in changes in art.