To complement my Korean learning, I usually look at Korean songs' lyrics and try to understand them. I've noticed that sometimes, Korean songwriters omit the verb 이다 in the sentences. For example, 난 그냥 사람 was part of the lyrics of a song, meaning "I am just a person", rather than 난 그냥 사람이야. There was no verb in the sentence. Since I've heard this kind of construction a few times I wonder if this is just a way of writing poetry/song lyrics, or if it's a way of speaking in a very informal way. I would be really grateful if anyone could explain the reason why this is done, and when it can be done. Thank you in advance.
Such omit is done in lyrics or poetry to make it rhyme.. But in spoken Korean you say 이다 /이야