I think the biggest reason people build or buy McMansions like that in Ontario is they aspire to live in a magazine. These kind and scale of McMansions are common as hell in certain US cites. The Dallas suburbs being one in particular. It's a social status symbol at a certain strata of society.
Notice nothing is special, or personal about it? No workshop for the guy, no hockey rink or basketball court for the kids? No hobby room.
I have a super rich relative who designed and built a 10,000 sf (or so) house. she has a gift wrapping room! Because she LOVES being social, Christmas, hosting birthdays etc and loves giving beautifully wrapped gifts. It's maybe the size of a small kids bedroom, but it has a use for her. she also has the nicest root cellar/cantina because she loves to can, preserve and pickle foods. Her husband loves to mow the lawn! He jsut says there is something relaxing for him to make these beautiful patterns. So he has extensive lawns and a separate "driving shed" for his little fleet of riding mowers!
They love each other but each has differernt sleep habits. so they built a 3 bedroom Main bedroom! They can go to bed and fall asleep with each other to stay close emotionally and physically. But they each have a small side bedroom they can go to later if they want or need to read, or sleep in or whatever.
And they LOVE to entertain so they have big common rooms and many small guest bedrooms for out of town vistors who might not want to drive home that night.
To me, their wealth is well earned and utilized in a big house. Same with some rich Muskoka and other cottagers with big spreads. They wan their kids to bring their friend to their place where they are safe and don't fall in with the wrong crowd. So they use their big money to build a fancy boathouse with a big room above and lots of water toys erc so their kids ddon't ahve to go looking for fun elsewhere and maybe get in trouble.
so, yeah, I can see it.
I live in a condo that is bigger than I need but I love the location and view. I miss having a house with a workshop, nice garage, library and room for my 'stuff'. But big houses and cottages are a lot of work... just to hire people to keep up the property.
To each according to their means and desires. I'm ok with that.
But that mississauga house in the OP is fucking soulless and gauche. that $20,000 commercial range has never heated up anything more than Kraft Dinner or some Fresh2go meal kit