How many people really met in record stores or arcades? I'd usually just go there with friends. I knew one person who met their husband in a comic book store.
As for transit, that is a huge US problem for sure. But don't blame the Internet or phones. Look at videos from the 50s/60s and you'll see just as many people silent on the train/tram/bus reading magazines or newspapers. By the 80s they'd have newspapers and the nerds would have walkmans. By the 90s it was more common for even-non nerdy types to carry discmans and now, everyone wears headphones. But that's always been there, it's not really new.
Death of retail: No social record stores, no social book stores, arcades
Internet everywhere: People on laptops at coffeehouse, on mobile phones at bus stop / checkout
Bad Transit/Urbanism/Public policy: Streets for cars, no plazas like the Italians, can't drink a bottle of wine in a public park