The additional time there is to give us an opportunity to process any refunds.
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.
There is a manual review after the payout has been initiated by the developer, and we can't guarantee how long that can take right now. 7 days is the minimum amount of time we require before the purchase can be made available, so it's enforced through the site.