As long as SmartTrack, or Crosstown LRT, go a short distance into Markham to Unionville, or to ACC in Mississauga, it will primarily serve Torontonians acessing job clusters there. Obviously, Markham and Mississauga won't pay for those sections. Btw, they do not ask TTC to pay them for the fact that they run their bus routes to Kipling / Islington / Finch / Don Mills subway stations.
Likewise, Mississauga will not pay for any service that just connects Torontonians to the airport.
On the other hand, if the LRT line goes all the way to Square One, it becomes a service primarily for the residents of Mississauga. In that case, it is only fair to expect them to pay the municipal share.