They do it on their own volition. It's like the Americans heavily investing in Korean security and more (Americans actually built the SK powerhouse of economy with American money in the 1960s, before that NK was actually doing better than the South) and stationing tens of thousands of troops non stop for 7 decades now with the understanding they're likely going to quickly perish in the event of the war resuming from ridicalously massive arty barrages and WMD attacks they expect NK to open with.
Actually it's nowhere even close to that what they have received and now pay back in a tiny part.
They do it on their own volition. It's like the Americans heavily investing in Korean security and more (Americans actually built the SK powerhouse of economy with American money in the 1960s, before that NK was actually doing better than the South) and stationing tens of thousands of troops non stop for 7 decades now with the understanding they're likely going to quickly perish in the event of the war resuming from ridicalously massive arty barrages and WMD attacks they expect NK to open with.
Actually it's nowhere even close to that what they have received and now pay back in a tiny part.