dude. if you got the talent to sing, not to compose, then you would really rather sing a cover song, than to compose a sucker song then sing? right? thats why pop artists, basically singers, do not really compose at all. They let song writers, do the job, and they do their parts as well.
While most bands (if not all), have the talent to sing and compose too.
They both do their jobs in improving opm scene, maybe, you just dont really like the way on how they do it.