'cause the songs are all perfection!
imo The Boyz's best song is Walkin' In Time, from their debut minialbum 'The First', and finding out that Primary was the producer was awakening for me (I love Primary's works).
Other Kpop songs produced by him that are simply amazing (and the fact that I love all of them is not a coincidence):
Lim Kim's Awoo
Uhm Junghwa's Ending Credit
J-Hope's MAMA (from WINGS album)
One of the best Kpop titles imo, MBLAQ's Smoky Girl, and also their B-side R U OK?, from their "Sexy Beat/Love Beat" album.
The entire Infinite H first EP "Fly High" - except for Victorious Way, produced by Vida Loca (an artpiece of an album, pls try this one if you've never listened to it).
He has also produced for Hyorin, JBJ, Brown Eyed Girls and Soyou.
I really want him to produce more tracks for Kpop artists!