Langstaff is 7km, straight line, has the support of the city councils, and except for a small stretch in old Thornhill is zoned for density increases. A line to MCC is longer, has a low density neighbourhood between origin and destination if a direct route is taken, if an indirect route is taken the route stretches even longer and follows a street which is a lower priority for intensification, and doesn't have large support from council. It is on the regions 25 year plan in York region, and not drawn on a plan in Mississauga. If you ask a bunch of people to design an extension of the Yonge line all of them will draw a line in the same place, you do the same in Mississauga and you will surely get a lot of disagreement. Until Mississauga and Peel put it on a plan, have the discussion about how density will stretch from the Toronto border to MCC, and pledge some sort of funding, the province isn't going to commit to it.