Very rarely, if ever, a song is completely made by a single person. In bands, lyrics, chords and melodies come from different members, some times separately, some times during a brainstorming session. Both bands and solo artists ask for advice, second opinions, some feedback to get that spark, and more and more people get involved. Also, there’s the production chain: who owns the studio, who is behind the label?
It is a lot to consider and bringing the subject during the composition process can feel very anticlimatic, but it is part of the job. Listen to Millicent’s advice in regards of song share splits in this episode of Success Beyond The Score: