@riot: Since ARAM accounts are back in the spotlight, could we get context on why "AR" isn't random?

Complaints about ARAM only accounts thumbing the scales in the mode (and now ARURF) by giving them a higher rate of strong champs have been around since ARAM launched, but as far as I know no one from Riot has ever explained why it is the way it is instead of a full roster for everyone, making it truely random. I'd love to hear a rationale for it