The additional time there is to give us an opportunity to process any refunds.
Viewing post in Payout review purpose
I just don't see why the two aren't combined. By the time a payment is eligible to be included in a payout, that should already be done. Again, if there's some sort of manual process involved, it could make sense. But, if not, there's no point in having two separate delays in the "collected by itch.io & paid later" method.