[olliej]

There's supply/demand - as some area becomes more popular more people want to move there. If you're not building new homes in the area at a rate that at the very least matches both the migration rate and the birth rate housing price is only going to increase. (People in SF fighting against tech folk also seem to fight new properties, ignoring that simply having children in SF means you necessarily must build more homes, maybe just a bit slower)

The thing that makes it worse is when taxable property values trail actual property values - it makes simply holding on to property a tax payer subsidized investment. CA for instance has capped taxable property valuations at 2%, which is a subsidy for empty properties, properties that increase rent/lease by more than 2% a year, and business (which never sell property) - the biggest component of civic services is fundamentally the cost of rent/mortgage, as that dictates how much all civic servants (emergency services, city/county administration, elected officials) need as there /base/ income. It also indirectly costs tax payers through the increased need for housing and other financial support for low income people (which can actually be a double tax, as it may result in tax payers paying rent on a property that is underpaying taxes anyway).