Canada

The problem really is twofold: yes, it is supply, but there's also an extreme amount of reticence to do anything about both supply and speculation.

This is largely because the profits of the current system accrue to people who bear experience none of the pain of it (which is also why healthcare is broken, and why transit is broken, and why nothing gets done about climate change). Taxes are kept low, assets keep going up and it takes very little effort to stay rich. And money talks.

"Building like mad" isn't going to happen because "building just enough to stop people from rioting" is more profitable. No builder is going to build public housing when they can make more on McMansions and condos, and no homeowner or speculator wants to see policies that would increase their tax burden or decrease the value of their asset.

Building like mad would help, but you'd achieve similar effects by smacking down the investment side of the problem, without requiring the government to, eg, directly buy equipment, supplies and employ tradespeople to build homes, which they'd have to do as bribing developers to do it doesn't seem to work. Plus, if you tax speculation hard, maybe you can use that tax revenue to build?

The real, core issue, though, is housing in Canada at the moment is the perfect neoliberal failure, and our policymakers are so wedded to neoliberal orthodoxy that the solution (massive, direct public investment) isn't just heretical, it's inconcievable. Most of our MPs/MPPs/MLAs and civil servants don't even remember a pre-Reagan/Thatcher era of massive public investment. They don't seem to understand it's even an option.