My husband and I are in contact with people there as we want to adopt/ rescue a sapsal. They tell me dog eating began in 1980 and is not a long standing cultural thing at all.
I saw dog offered as meat at a butcher shop in Uijongbu in 1978. Only time I ever saw that in two tours there and I got around quite a bit.
Before Criticizing South Koreans Eating Dog, Know the Context First
https://www.koreaexpose.com/eating-dog-meat-industry-south-korea/