IDK, I can see both sides of it. Boys Da Capo (BDC) never took off and have been disbanded for two years. The trademark was probably worth more being sold/transferred (I highly doubt Rhymer just went "sure, do whatever you want"). I can understand them wishing the company they used to be signed to kept it longer, but ... IDK how long is considered a reasonably "acceptable" period of time to keep a defunct trademark. And I'm assuming Korea has similar laws to the United States, where unused trademarks are assumed abandoned after a certain time anyway (Google says it's three years, so they wouldn't have had it much longer anyway).
It's definitely one of those situations where you have both business and emotions tied up together.