Let me explain why.
When you play arena, you can be matched against opponents from your own faction and the enemy faction.
When the season is over, the R1 players are determined for each faction, which is pointless since you’re fighting your own faction as well as the enemy faction.
Cross-faction arena should be a thing, so we can finally get rid of faction racial imbalance and increase arena participation, which is at its lowest point currently for reasons not relevant to this thread.
Combine R1 for alliance and horde as well.