So Garth Brooks is a creature of the Nashville country music industry. The Nashville machine has not followed the trend of promoting songwriting bands to anywhere near the same extend as the LA record labels have. Criticizing a country music entertainer for not writing his own songs is like criticizing a magpie for having white stripes. There is indeed great value in songwriting bands. To the artist (or whoever has contracted the rights to the artist's recordings), it means double the royalties. To the record companies it helps diminish the power of ASCAP, which used to function much more like a proper union than it does today. The expectation that a band should write its own songs was first cultivated in the 60s in an audience of baby boomers, using baby boomer bands. It's about as boomer as bell bottom jeans. That doesn't mean it's in any way bad for a band to write its own songs, but division of labor between songwriters and entertainers was the norm before that, and continues to be in many musical traditions.