Every player bans one champion - and so those picks would not be in the random champion pool of everyone else. So if there’s something that’s just way cancer you could at least remove it from your ARAM games for a while. Or if you just get sick of seeing something over and over.
Some champs were banned so often that bans in ARAM were tantamount to completely disabling them from the gamemode. Riot thinks that every champ should be playable in ARAM, so they chose to look into alternative ways of balancing these problem champs, which ended up being the ARAM-specific buffs/nerfs.
That’s exactly what I’d like to see. Certain champs have no place on ARAM, like Shaco or Teemo since the removal of oracles. They are literally the Antichrist of fun.