Frankly to answer the question posed: Why are there so many lyric-only folks? - It's because there's less time involved in being lyric-only. We all have other interests and obligations in addition to our music pursuits. Those who have less distractions from music tend to do better if they have the talent, persistance, and work "smart". Those who learn to play and compose music have a larger time requirement to dedicate to their craft, because learning music and learning to play music takes time. Many don't want to or are currently in circumstances where they can't set aside the time necessary. It depends on one's personal priorities. I agree with many of the comments on this thread about lyricists learning to read and play music themselves as a means to improving their craft. It's a matter of learning the perspectives involved in writing and (for those who expand to performing)singing songs. The more working knowledge one has from actually participating in all aspects of the creative process, the better potential they have for writing a hit.