So for people to get high scores in a scenario that isn't the normal metric would have to be an entirely separate scoring sheet, basically, lest people be cheesing it. Riot is pretty tight-fisted about letting those loot boxes go.
I'm thankful we get anything in ARAM. Haranguing them over minor details like 'I can't S massively overplayed champs' feels a bit like having our cake and eating it too-- realistically, getting rewards in ARAM is kind of cheesing out already, considering how much different it is from Rift and how removed it can be from that experience.
The ranks just aren't that important to be splitting hairs like that. It gets to benefit from the same rewards? It gets to stay on the same metric.
Oh, and you probably wanted 'Invites.'