That is a factor.
We must also remember that for technological reasons, there was a time when flights from Europe could not go any further than Mirabel on the North American continent. That was one of the reasons why Atlanta became the biggest airport. Several years ago, airplanes began to have the technical capacity to make it to Toronto and then even further.
Of course, access is a factor as well. Highway 13 was never completed and there was no rapid public transit link. But there were also technological reasons. There was also the fact that the choice was made to build an airport without boarding platforms and passenger transfer modules. That may have been a false good idea, which was almost never repeated elsewhere.