In some parts of Vancouver city proper there are mansions, but mostly even newer houses are 3-4k sf and the larges ones are in suburb cities where land is cheaper. Mostly - but there are still plenty of large houses in Vancouver, and ones with suites.. it's just way more common in the suburbs where the same or lower cost of building builds a larger house with multiple rental suites instead of a nicer house with higher end e v e r y t h i n g for finishing materials.
I suppose we have land space to a degree.. however, part of the reason everything is stupid expensive here is because there's only so much land between the ocean and the mountains to build on - and a bunch of it is, and should remain, ALR (agricultural land reserve) for local food supply. There are ever more homes being built in the mountains, but not a major sprawling city like Vancouver and it's suburbs - there isn't another large flat piece of land like that maybe anywhere in BC.
Things get built big because there are a lot of wealthy people that have moved here that like to show off their wealth with very large homes/estates. It's become a "thing," in Chinese business culture to show off your "Vancouver house," to your clients.
Some local people who have made $$$$ in a generation or two like to show it off with their massive farmhouse mansions - seriously - one could take a driving/motorcycle tour of farmhouse mansions across 5 or 6 suburb cities and be absolutely gobsmacked at these places.. some of them almost don't even look real they're so "straight out of the movies," - especially when they're lit up at night. I read an article that some Chinese Billionaire's sprawling farm estate out in the valley has security drones flying around the perimeter keeping an eye on things.
As for "regular," big houses.. they're built for multi-generational Indian families and/or to have mortgage helper suites because it's almost mathematically impossible for one or two incomes to make a mortgage payment anymore. So, while we still haven't managed to get rich people on board with building more condos/apartments, there are at least multi-family houses being built that do tend to house more than just an immediate family. Some places are large enough to have 4 separate suites in the basement, then 2 floors of a family home above.
MR sold his Vancouver home after his wife died.