Now that coins can't be redeemed for cash, what is the purpose in still taking a percentage of the coins from each match?
We need to ensure the coin economy stays stable. For that, the number of coins that get created overall should be roughly equal to the number of coins getting destroyed. Otherwise you have runaway inflation, which would cause all sorts of problems.
Every time the coin wheel is spun, coins are created. So you need some way to balance that with coin destruction.
I have plans for better ways to accomplish this in the future, but for now that way is the percentage you speak of.