In a world in which every car, bus, train, and building is air-conditioned, and in which more than 90% of people in Texas are fat and flabby, an underground pedestrian complex was always a non-starter. Montreal residents need to escape the snow and cold, just like the residents of Kyiv, but the residents of Dallas don't need to go underground to escape the heat thanks to all-pervasive AC. And as for walking... the average US citizen walks less than 5km per week (this includes all trips to the coffee machine, waddling from living room to toilet, and so on) and in Texas this average is certainly lower as there are no outdoorsy types to boost the number of kilometers walked.