Auto insurance rates are something that I had never thought of contributing to Brampton's transit ridership. Even with good transit service, it always struck me as a bit odd how high the ridership was because the city is just so totally auto oriented. I can definitely see auto insurance rates effecting that,. For low end auto owners (people driving 15 year old Civics, etc.), auto insurance is usually the greatest cost.. if it's double the normal cost in the rest of the province, I can see why a lot of people switch to transit.
Here is an article on what system changes Brampton Transit did.
https://www.strongtowns.org/journal/2018/11/28/a-suburban-model-for-incremental-transit
What that author omitted is that Brampton has the most expensive car insurance for a "standardized driver", but the reality is even worse, because the typical Brampton driver is younger, and has less experience than even the younger age would suggest. It is entirely normal in Brampton for a driver under 25 to be forced to pay $500 a month for the car insurance for a $2000 car. So right there, Brampton Transit has a significant cost advantage. Brampton however has other significant factors for example population density. While one might think that the suburban hellscape of Brampton, composed mostly of detached single family homes, would have a low density, due to demographic factors the detached single family homes actually have a density that one would expect in townhouses. Brampton has a lower individual income compared to the rest of the GTA, this is counterbalanced by many houses having more than two wage earners in the household, but this causes issues for car transportation, as they can't afford 3 cars, and even if they did, they only have space for two cars. Basement apartments are pervasive in Brampton, but given the number of international students has been completely exhausted, in the past couple years Brampton has started having lodging houses appear, in both larger numbers, and more people. The most recent publicly stated record by the City of Brampton is 27 people in one house, and at this point a dozen people living in a lodging house is now considered "normal" by by-law enforcement. This leads to ridership growth in rather random locations, for example the 4 Chinguacousy had a.m. peak ridership grow by 68% from 2016 through 2018, now it has ridership around 13k a day, which made it go from planned between 2031 to 2041 for a Zum route, to 2022, displacing the planned Bramalea Zum.
tl;dr Brampton Transit did good work to get good ridership growth, and it has been massively boosted by outside forces such as population density and car insurance that is too damn high.