It's because the BC Interior is treated like a vacation spot for Alberta oil money.
There are a lot of seasonal residents who live and work in Calgary, who own summer properties by the lakes in the Okanagan, and these "outsiders" are seen as not having any stake or investment in BC. They're perceived to be loud and boorish, polluting the lake with power toys, etc. Never mind that in reality, most people doing all that are locals...
The economy in BC outside of Vancouver is hurting. Unemployment may not be high, but all the jobs here pay close to minimum wage and most locals are unable to keep up with the rising cost of living. Alberta money is seen as contributing to these rising costs, as real estate has been gobbled up by rich Albertans. People who live and work in the the interior can't afford rent, meanwhile properties owned by Albertans are left sitting empty 8 months out of the year. So there is an element of resentment there as well.
Very similar to the animosity against Chinese money chasing after Toronto real estate.
I know a few people who left BC and moved to Calgary for the better costs of living, yet Alberta treats them well. Why would BC have a thing against Ontario, or the rest of Canada? Even the slogan "The Best place on Earth" is pretty arrogant IMO. I know places on Earth that are much better.
As for the living costs, a lot has to do with chinese/overseas funds, I have family there who got approached by a car outside their house, chinese lawyer in a car, offered double value on the house, cash. They sold it, and still live in it, it's just parked real estate. I know 2 other people that had this same thing happen, one sold, other is waiting to retire.
I tried moving there for 3 years, went back and forth, and one day would still love too, just now I know, BC stands for Bring Cash. The people do scare me away, and lack of diversity