There are many causes, but supply shortage is the most significant because it is now an suppliers market.
Many property developers went bankrupt as a result and some others have not been able to enter the market since. Much of the current construction is now commercial and not residential. Accommodation builders are more interested in Student Complexes than family homes.
The authorities stopped building any social housing. This put pressure on the private sector to rent.
Bedsits were outlawed to eliminate the lower market. A number of factors have led to the abandonment of accommodation over shops.