Canada

The primary cause is that we've put a lot of focus on making life, in large cities in particular, around those houses much more livable.

We like to talk about how cheap those city homes were 50+ years ago, allowing you to buy them for a song, but do you remember how awful cities were back then? They were industrial, crime-ridden nightmares. Homes were cheap because nobody wanted them.

Things have changed dramatically over the past 10-20 years. The messy industry has mostly left, often replaced with businesses which provide enjoyable actives (restaurants, shopping, entertainment, etc.). We've made great strides in reducing car dependance, improving mass transit and cycling options. Crime has plummeted. The list goes on and on.

AirBNBs, etc. have come into existence for the same reason: People today actually want to be there. That is your primary cause. Desirable things are more expensive than undesirable things. That's the way it goes.