The photo in the article looks to predate the mass adoption of cars. Maybe it was because of new engineering capability + attempting to avoid the elements?

It's probably both. The picture in the article is very early days and was then a proto-PATH that was probably first built to deal with an acute problem (probably crowding on the sidewalks as the streets started to be taken over by vehicular traffic).

Toronto's PATH doesn't have a central control or planning system. It is literally a series of 1-1 agreements between buildings that build tunnels under streets to connect themselves. The main benefit to each building is that they can charge retail rents in their basements for through traffic. The system map was terrible and even had a planned route prematurely showing a way to the Eaton centre from the south for a building that was left uncompleted for almost 30 years (work stopped in the early 1990s recession and was only finished right before COVID hit).

Avoiding the weather for commuters coming in on the subway and GO train (suburban commuter rail) was a nice benefit, though only very recently was Union station fully separated from the elements. The one problem with PATH is that the shops are completely targeted to 9-5 work commuters, particularly to finance workers; think coffee/business suits/lunch/etc. Though portrayed as a giant mall, almost all the shops are closed on weekends and don't stay open much into the evenings (Montreal's is more dynamic comparatively). COVID of course upended the business climate of the shops, too. Some newer condo towers have been connected and there is some very early signs of something more dynamic, but the towers seem to still be holding on to the idea they can charge pre-COVID rents. My personal opinion is they should be seeing this as a loss leader to convince people to want to come in 5 days a week (cheap, good lunches, etc).

Anyways, we'll see how it continues to evolve.

The first one was built to connect two of the same company's department stores (Eaton's, now defuct, but once an iconic Canadian chain).