One of the reasons the idea was sticky is that 90% seemed like a significant number, almost all the way to 100%. Where there's nothing so obviously magical about 10 or 12 months.
Now, people will argue that, for many, the value of their house will be higher. That is true, but the same applies to governments. Infrastructure such as roads has value.
Traditionally, in many countries, the state also owned airports, water pipes, and electrical wiring that brought in money. That, I think, is where the real problem lies for some countries: they have sold the stuff that brings in money without bringing down their debt.
"Getting a mortgage of 3 or 4 times one's yearly income..." One of lessons of the last ten years is that people, businesses, and governments can very easily get loans they have no ability to repay. And too often, the borrowers have to default. This is bad for the borrower.