If you take population growth into account, Brampton's transit ridership growth hasn't been that different from Mississauga, Toronto, Waterloo, London, Kingston, and other Ontario municipalities. For example, from 2003 to 2014, before the LRT construction began, the ridership of Waterloo Region increased from 29 to 49 per capita. Brampton went from 22 to 36 riders per capita during that same period.
From 2003 to 2017, Brampton's transit ridership increased from 22 to 45 per capita, Mississauga 38 to 51, London from 50 to 60, Kingston from 25 to 35.
Brampton spends around $100 per capita annually on transit operations, the same as Mississauga and York Region. Brampton Transit net operating budget is around $70 million annually, MiWay $80 million, YRT $110 million.
I think if anything York Region was the most aggressive adding transit service. The introduction of VIVA was like 40% service increase in one year. But the ridership never materialized. York Region spends 40% more on transit operations than Mississauga but Mississauga has 15% more transit service (1.3 million service hours annually for YRT vs. 1.5 million for MiWay). Sometimes lack of spending is not the problem.