The problem is that "drive less transit more" is only an option if you live where transit is viable. If they were simultaneously investing money (or even reinvesting the carbon tax into) into subsidies for transit systems, cycling improvements, walkable cities, and the like so that these alternatives are accessible to everyone then there would be at least a carrot to go along with that stick. But there's virtually no amount of tax that will ever make trading a 30 minute car ride for 2 hours on and off with multiple transfers with the bus a reasonable alternative. And there's no way to get more people into buses or trains that are crammed full to the point of skipping stops even if you could somehow convince people to make that trade.