Because the perks do not offer an advantage in the economy. Thats it. That is the reasoning.
You say "donators can make more money in minigames and selling quartz".
1. You can sell quartz at most pwarp shops for more, so no.
2. You can make the same amount depending on how many games you play, and during the game, everyone has equal chance to win. The perk is a time saver, not money maker. As muunkee stated, its a convienence.
We have many cits richer than ults.
Also, it does not matter if you believe us. If we were in voilation, we would have been shut down already.