I had the feature for a few weeks last and early this month (i currently don't have it and i don't know why). What i noticed is that the early payout option was only for orders that clients marked complete after delivery. Anything that was automatically marked complete after 3 days didn't have the option.
I guess it's a security measure for them - clients that complete an order themselves are usually satisfied with the quality they get. Chances of them asking for a refund is very low compared to a client that did not complete the order themselves.