Lots of people want to move to Stockholm, Malmö and Göteborg (Gothenburg), so demand is rising faster than supply.
But also, the laws that ensure that lower class people are to afford to live in nice places also makes it a bad investment to build new houses. It's great because the classes are more integrated, leading to more sense of community, less crime and less 'ghettos' riddled with crime and drugs. But on the other hand, since the government keeps prices reasonable, low prices makes it a less good investment. Sadly we can't have the best of two worlds, but I think a golden middle path ("lagom") is the way to go. Not regulated enough that no one will invest in houses, not free enough that the lower classes will (even more than it's now) have to move to ghettos.
Yes, non-availability. Basically high demand because of rapid urbanization, poor infrastructure, small and single city center. Low supply because of rent control on the first and second hand market, conversion of rentals and not enough new buildings. At least for the three large cities in Sweden.
A large factor is probably the oligopolies in the building industry, which earns lots of money with the present situation, despite little building going on.
Regulatory capture in Sweden is still not counted as corruption, for some strange reason...
Is it plain non-availability? If so, then why? If not, then why? (I'm genuinely interested)