It's not just occupancy. Conversion are typical when older buildings revenues are less than capital costs. There have been residential and commercial buildings with good occupancy that have converted from rental to residential condominiums because of a cap on how much they could charge for low quality space.
Calgary buildings are in great shape partly because rents were high enough to continually upgrade older buildings and partly because the inventory isn't that old. I believe office buildings owners will hold out for some time. The high rise residential market is in better shape but, it isn't red hot either.