Just as in game microtransactions, it doesn't matter how much or little the median person is paying, because all the profit is in the minority of very big payer

Just as in game microtransactions, it doesn't matter how much or little the median person is paying, because all the profit is in the minority of very big payers / 'whales', so you optimize the payment structure of the small payments to ensure that they don't prevent you from capturing the whales. If your game doesn't earn a million dollars, it doesn't matter to Epic, because all those (many!) tiny games in total don't earn enough that even a much higher pricing would move the needle. However, if the low-end pricing structure means that one more (or one less) blockbuster chooses this engine, that makes all the difference, because they are going to pay the full rate out of the billion dollars they earn.