I'd be interested to know what motivates these people to take public transit, while driving their automobiles would almost certainly get them to where they're going faster.
That's not necessarily true. Many TTC riders have a car but choose transit for the daily commute because it's faster and/or cheaper. I know many people who have a car and choose transit. They would not choose transit if driving was both faster & cheaper.
The two main factors that make the TTC faster or cheaper in some scenarios are: traffic & parking.
If Toronto had no traffic (like Detroit), then driving would be faster for every trip. With traffic, travel times become competitive for transit that bypasses traffic (subways), when travelling along subway lines and heading downtown.
Secondly, convenience & price of parking. In some places, parking is not conveniently available (you may or may not get a spot) and costs much more than a transit pass. If parking costs $150 a month or more, and transit is faster anyways, you may as well choose the cheaper & faster option. Parking can also be inconvenient when you have to drive a while through a parking garage or the parking is a far walk from your office anyways.
Of course, if you're working in a suburban office park surrounded by large & free parking lots near a highway with nothing but bus service, car is the obvious choice. But if you're like John Tory and have to commute St George station to City Hall, why wouldn't you choose the more convenient option, even if you have all the money in the world.
It's the same in any major city.
The other thing is, even if you're making a very good salary, you may decide not to buy a car and buy a house in a transit friendly area. If you also work near transit, it can work out. And even if you make >85K a year, as we all know, housing is expensive here.