The screenshot was taken from a live stream at 1:30pm on a Wednesday, not during long-weekend rush hour.
The Gardiner, just like the 401 and the DVP, are a traffic nightmare nearly all the time, yet they don't have bike lanes on them.
This isn't some strange coincidence or conspiracy.
Car dependency, rather than people riding bikes, taking public transit, or walking, is the real problem causing traffic and gridlock.
Roads do have maximum capacities and bottlenecks, though it is true that driver behaviour can make it worse. Or rather, makes it worse faster.
If an exit can only handle 50 cars per minute but 60 people per minute are heading down the highway towards that exit, that exit will back up by 10 cars per minute. Asshole drivers might further reduce the capacity to 40 cars per minute by doing last second lane changes that force people using the exit to slow down more or hit them. And they might slow down cars not headed for that exit when they need to slow or stop to find a gap because they tried to skip the line.
But at the end of the day, if the exit can only handle 50 cars out of 60 wanting to use it every minute, it will back up, and it will only take 5 minutes for there to be an extra minute worth of cars waiting to go through it, even if everyone is driving optimally.