[Doady]

The problem with commuter rail in the US is the same as the problem with the light rail there: they are isolated systems and lines, agencies treat them as isolated, and people in this thread talk about them as isolated. GO Transit in Toronto has high ridership because it is just a very small part of much larger transit network. Most of the ridership in suburban Toronto is on buses, not commuter rail. Even 19.5% of GO Transit's weekday ridership is on buses.

Philadelphia's commuter rail got 134.5k riders per weekday in 2019, representing 12.6% of the weekday ridership of Philadelphia's system. Although Toronto's GO Train system got almost double that ridership, 230.5k boardings per weekday, those 230.5k boardings represented only 5.4% of Toronto's transit ridership. Double the ridership, but half the importance.

SEPTA bus 508,400
SEPTA heavy rail 329,200
SEPTA commuter rail 134,600
SEPTA light rail 89,400

TTC heavy/medium rail 1,620,300
TTC bus 1,281,400
TTC light rail 530,600
GO train 230,500
GO bus 56,100
MiWay bus 201,287
Brampton Transit bus 144,523 (2016)
York Region Transit bus 101,993 (2016)
Durham Region Transit bus 51,841 (2016)
Oakville Transit bus 13,800

You can see similar problem in Chicago. In 2019, Metra got 274.0k boardings per weekday while Pace Suburban Bus got only 135.2k boardings, less than half. Compare that to Mississauga's MiWay bus system which got 201.3k boardings per weekday or Brampton Transit with 144.5k, together almost three times the ridership of Pace despite serving less than one-third of the population. The untapped potential of rail in the suburbs is because of the lack of the buses in the suburbs.

For a transit route to be truly successful, it needs to connect to as many people as possible, workplaces to homes especially. That doesn't just mean TOD and high density, that also means routes need to connect to as many other routes as possible. Shorter walking distances also requires routes to be closer together. You need lots of local transit feeding into all those suburban rail stations, and the cheapest way is with buses.