Too suggest that the specific, most popular brand of wine at that time was a fluke is to tell those who bought it they were going against their own will is sort of silly? They were simply buying what they like makes more sense. To say that whats more popular has changed over time, is another larger subject.
It would include the fact that whiskey has again gained popularity too and that brewing is at the stage of what happened? I'm old enough to remember when there were zero craft breweries, small towns in some states having a brewery and the only people who brewed at home were from certain cultures like Germany, etc.. I worked in a supermarket for nearly 6 years and we sold Blue Ribbon malt, caps, etc. and there were virtually zero wine making or brewing suppliers back then.
Yes Riunite lambrusco was once extremely popular and still holds plenty of shelf space to this day in liquor retail shelves. I could thrown into the conversation all the stuff I don't like: rhubarb, rutabagas, turnips, parsnips, certain wines and beers like Corona which is quite popular?
A Lambrusco kit might be back sweetened to suit my purpose and taste is a great conversation in my direction if the juice got me what I want flavor wise.
Meanwhile,you and others are free to like what you like. We use it for one specific purpose and i can assure you most Sangria is not mixed with dry wines.
Like Paul Harvey said, that's the rest of the story...