Since language has the same structure as the unconscious, trying to be something we are not isn't as easy as we might think.
It was easier for artists to deliver genuine hopeful and positive messages in the songs they wrote when they were 17. If they try to recreate the magic when they're not in that place mentally anymore, it will not be convincing. For any attempt to moralize, harsh judgments will leak out somewhere else. Any attempt to be masochistic, sadistic will wait right there in the corner. This is why writing from the heart is more important for personality development than writing to be captivating. The goal is to find blind spots, not to teach a lesson.
Taylor Swift, however, sucked from day 1.