The great myth that people keep believing is that improving local transit in suburban cities/towns will reduce the number of people driving to GO stations. I offer as an example the downtown Brampton station.....it is served by not one but two very frequent bus routes (by suburban standards) the combination of regular and Zum buses along, both, Queen Street and Main street means that on both routes there is no need to consult service schedules...there is a bus, of some variety, coming every few minutes during peak times.....it is how I get to the GO when I use the GO.......but do not kid yourself, I am (by far) in the minority of people getting on (or off) the GO at Brampton and heading to/from a bus. My observations are, obviously, anecdotal, but I am pretty sure the numbers are supportive of my observations because GO has purchased and is about to demolish an office building to provide more parking.....they know their audience and know their users...and they are people who want to drive and park before getting on a train.
Add in that, I imagine, the off peak user is probably even less likely to use transit (partly because they are likely less regular users and, therefore less familiar with it and partly because frequencies of local busses drop in off peak hours) and I bet the move to build garages is because they are investing billions to provide off peak service on the other rail lines and their only way to get any riders on those trains is to have somewhere for those off peak users to park their vehicle.