If I'm putting 90% of the value, why don't I just add another 10% and buy the property outright? Are there restrictions on who can buy a house/apartment in Korea?
Usually there is a monthly management fee that ranges from $50 to $100+ dollars that covers cleaning of common areas, repairs, etc.
Many South Korean landlords are underwater on a bad investment and use the next renter's deposit to pay out the last. Citation not possible.
The point of the system was to spur investment in the south korean economy.
Of course that prior speculative bet could be in mortgage(s). You would need to look at other weakness in that economy to rationalize whatever bet you want.