The housing crisis basically everywhere has nothing to do with a shortage of housing stock or tourists and everything to do with boomers and gen-Xers storing their wealth in property. They do this because they know that the government will bail them out, they won't allow the property market to crash. Coupled with the income and the investment vehicles that allow pension funds and private investors to purchase equities backed by property, it makes investing in property at scale more liquid than simply buying second, third, and fourth homes to rent out.

Spain, Portugal, and Italy are in particularly dire straights due to the wealth inequality between generations. Spain in particular is the worst offender in Europe, where Gen-Xers were the last generation to receive fat pensions. Spanish millennials simply cannot afford the rents charged by boomers who simultaneously import cheap labour to undercut the salaries of other people's children, meaning wealth accumulates in families who were able to get onto the gravy train.

In a free market you'd have a lot of construction, including affordable homes, but the people who vote make sure they don't build enough to bring down house prices, nor to disturb the local scenery around their own homes.

This all means that younger people who can save, locked out of the property market by the scale of the deposits they are required to have saved, invest in stocks and bitcoin because these are assets they can take with them and liquidate in places that make it easier to purchase homes with decent salaries. That's why these Mediterranean countries, although clearly not the only countries experiencing housing crises, are the oldest countries in Europe demographically. The young people are just opting out.