system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is the purpose of singles in the music industry?

For a very long time I thought singles were supposed to be previews of an artist's upcoming album. I only just realized that this wasn't the case when two artists I listen to (Macklemore and Linkin Park) released singles off their new albums well after their the albums were released (Can't Hold Us and Castle of Glass respectively). Thanks for anyone who can answer this!
gpt
Purely to make money.

The singles release to great fanfare, get fresh radio plays, people who didn't hear about the album might buy them.

They normally have demos or stuff that didn't make it on the album to persuade die-hard fans to shell out for them.