"Vacancy" is something above a building being empty. Vacancy is a building that has space available that hasn't been filled. It does not cover buildings deliberately left empty by owners. A building waiting years to be demolished and replaced isn't vacant, nor a condo kept only as an investment and never lived in.

That mall in Calgary isn't vacant either. Each store/stall is technically occupied by its owner. There just aren't any flesh and blood people in the mall.

NYC has ~60,000 buildings. Less than 1% of them are deliberately left empty by their owners. It’s a very different situation in a city which can make use of that space as demonstrated by the low vacancy rate.

That mall does have people shopping in it. In terms of retail square footage it’s underutilized but a long way from empty. Good or bad investment they are not building 3 of them next to each other while the first is far from full.

Really, you have some edge cases with people trying to time the market, deal with zoning or lawsuits etc. But, that’s different from seeing 6 empty apartment buildings and saying let’s build another one.