quarantine is not mandatory for vaccinated domestics only. there is talk from various business sources that Asia should “prepare to lessen quarantine restrictions” in the coming months. But because there is no universally accepted way to document vaccination, Korea has yet to change international stance on quarantine. And their goal at the moment is getting their population vaccinated, without inviting any other variables that could cause complications (such as lesser restrictions, which they tried earlier this year, and which backfired dramatically).
I have a relative who is a geneticist hired to work on the pfizer vaccine. Though I doubt her input is really that absolute in the way of politics/diplomacy, she did say that international restricts are often the last phase of disease control consideration, because you can’t guarantee that other countries are doing the vaccine the way that you are domestically, and because coming up with a universal vaccination document/passport requires and enormous collaboration that individuals countries don’t have the time for in the beginning of pandemic recovery. I would except quarantine to be lifted for all vaxxed travelers late this year, potentially next year!but that’s just an inference