This feels like it should be illegal. Just by random chance there will be a point in time where enough tenants ask their deposit back at the same time, and you

This feels like it should be illegal. Just by random chance there will be a point in time where enough tenants ask their deposit back at the same time, and you enter one big economic crisis. Of course, banks also have this risk of a bank run, but the difference is that big banks are tightly regulated and have a strict reserve rate they have to abide to (usually >5%). I wouldn't trust a big population of landlords who manage their own finances, and have a big incentive to cut corners. If anyone knows a method to short Korean housing, please let me know!