If the parents run away SOMEONE has to pay the loan. There are legal money lenders, but as you can guess, the ones depicted in manhwa are often on the other side of the law.
They put down their family members names as a sort of collateral, so they would be scared to run away or stop paying the loan, in fear of the sharks going after their relatives. Like a guarantor. However with trash parents that don’t care about their kid, it’s tough luck for the child.
Illegal sharks do not care about your age or ability to pay back to loan, they will get their money somehow ☹
But from what i know, in real life this is not as common as it seems it manhwa and kdramas. Legal lenders are more common. In that case the loan may be transferred to next of kin, but you are able to renounce inheritance, declare bankruptcy etc.
Idk if this a Korean thing or a mostly everywhere thing (Global? Universal?) or it's just fiction, but if people cannot pay off their debt/loans why does their kid have to pay for it in the parent's place??
Kids can't earn & make money until a certain age. The kid is living their own life once they become an adult, that's their money, not the parents.