Mostly societal accumulation of wealth and consistently low interest rates (which are low in part due to the high ratio of accumulated wealth to productive capacity).
Housing becoming an investment rather than somewhere to live in.
Why is Bitcoin so overvalued?
Once it becomes a "store of value" the price just goes crazy.
That shouldn’t affect the price of rent though. Landlords are largely price takers and have no pricing power. But rents are also going up.