Is only a handful of specific champions avaliable every day in ARAM?

Was just wondering, is this how ARAM works? I don't play it a lot, but the days I spam it, I always get the same champions. A few days ago, I got Xayah 3 times in a row (if I didn't have her, a teammate or somebody in the enemy team did) and today, there was an Olaf, Lissandra, Lee Sin and an Urgot in every game.