It's because before the game was released you used to get 5 gold for every win. They later changed that to 10 gold per 3 wins, but they kept the increments of 5 for arena rewards.
Instead of changing the rewards for arena I would suggest they change it back to 5 gold per win.
Assuming your question wasn't rhethorical:
It's because before the game was released you used to get 5 gold for every win. They later changed that to 10 gold per 3 wins, but they kept the increments of 5 for arena rewards.
Instead of changing the rewards for arena I would suggest they change it back to 5 gold per win.