If anything, the golden age of third places coincided with the golden age of suburbanization, which was obviously heavily car dependent. Their death almost certainly has more to do with financialization making it harder for small businesses to stay afloat, a drop in demand due to competition for attention, and decreasing work-life balance eroding people's ability to socialize.

In my grandfather's day, one income was enough to support a household, and there was less free work being done on the job, which meant fewer hours and being less drained at the end of the day. And yes, people spent less time commuting, meaning they had more time and energy for socializing after work. But communities were also more decentralized, and population centers had fewer people in general. A big part of the problem is that modern cities can be massive, and invariably funnel people to a handful of work districts, which just doesn't scale. When you double the distance to the CBD, you quadruple the number of people coming in (give or take, it's not exact because we tend to increase density close to the CBD as a response to this). Take it from someone who's lived in a place where cars aren't really necessary, the logistics of urbanization are still a crap experience when you're crammed into a train carriage during rush hour. It's common for people to commute for 90 minutes on public transport in Asian megacities, for example.