They know as a foreigner in Korea you attract a lot of attention and they may assume that you must have many girls chasing you.
Even when a Korean girl is dating a Korean guy, parents have significant power in manipulating her choice of a potential husband. Korean girls seek their parents’ approval and may end up breaking up with a guy if the parents disapprove and tell her to break up.
A Korean woman depends more on her family for support than a western woman.
Koreans tend to live with their family until they are married off in their late 20s or early 30s.
When a Korean girl dates a foreigner, they are scared that their new boyfriend may think they are easy.
So, Korean women may be more cautious dating a foreign man than when dating a Korean man.