You do get a collateral with Jeonse. You will have claim to the property under the insolvency law.

Of course there might be competing claims that may take precedence. Usually mortgage or prior loans. So you are supposed to do research on the property before signing a jeonse. There are also insurances for Jeonse as well.

Having said this, I still agree that Jeonse is crazy. I think South Korea is due for a huge painful recession when the housing, construction and capital market collapses due to Jeonse domino and the Legoland fiasco.