Public transportation costs to build and operate, which means more taxes which are politically difficult.
On the other hand people have shown again and again that they are willing to spend tens of thousands of dollars every year for what the car gives them.
Private car transportation is also massively subsidized. Near my neighbourhood, they are rebuilding a highway exchange for more than 3.6 B$CAD (2.7 USD). A few blocks from there, they have to rebuild a bridge, another 4.2 B$CAD. It's not even old infra. It was built in the 60s, but it didn't last (harsh winters, bad concrete, too much traffic).
And that's why they have gas taxes. Canada has a federal one, and maybe your province has an additional tax.
In Vancouver, public transportation gets half it's funding from property tax and fuel tax. And more than 70% of commuters drive. So not only are car drivers funding roads, they're also funding public transportation.
For Quebec, according to some numbers I found, in 2013-2014 (when gaz prices were high), the provincial government made 2.2 B$ from gaz taxes that year. If that's the case, it's not that much compared to all the infra that needs overhaul.
On the other hand people have shown again and again that they are willing to spend tens of thousands of dollars every year for what the car gives them.