Even if a large proprtion of transit riders in York Region could walk to Steeles and every single one of them would be s YRT rider if the TTC did not exist, is it the TTC's fault that York Region does not pay at all for that bus service along Steeles the same way it does not pay a single cent for the maintenance of Steeles Avenue itself? Is it the TTC's fault the YRT has the highest fares in the GTA? C'mon.
MiWay the New Mississauga Transit seems to have no problem maintaining high ridership and frequent service for its routes in Malton, YRT should be no different. And indeed, one of YRT's busiest and most successful routes is 5 Clark Ave, which runs very close to the Steeles corridor. The TTC is not inhibiting the success of YRT in any way. With easy connections to various TTC services and to York University, YRT arguably should have become a system with moderate ridership and moderately frequent service.
Personally, I think it's Brampton that is in the worst situation in terms of growing ridership.