Object structure

There is no explanation as to why users has 1, while profiles is not numbered: 
const profiles = [
  {
    id: 1,
    userID: "1",
    favoriteMovieID: "1",
  }
]
Verses
const users = {
  1: {
    id: 1,
    name: "Jane Cruz",
    userName: "coder",
  }
]