Performing on stage, appearing on TV, and promoting products isn't the only way K-Pop idols make a living. Some of the most popular idols are also in fact very talented songwriters and producers, which is why they are able to rake in huge profits from copyright royalties.
Since they make a living by performing good music, it makes sense for them to also make good music for themselves and other idols as well.
Below is a list of K-Pop idols who have the most songs copyrighted under their name at the moment. (As of February 2018)