Why should I listen to songs in Spanish?

Because it will massively improve your vocabulary and grammar. You'll have a context for the new words and sentences you're learning; you're far more likely to remember words if you learn them in a song rather than in a long vocabulary list.  When you’re trying to learn a new language like Spanish, it can feel repetitive to sit and learn all the lessons from a book without really experiencing the culture. Traditional learning might also make it more challenging to memorize all the vocabulary words.