I agree. Some buyers might find a project, buy it on a whim or download free without tipping, realize it's amazing, better than they expected it to be after they download it and experience it, and want to tip *after* having experienced it. I can see this being useful both for myself as a creator, and as a player who has been pleasantly surprised by several of the games I've bought, only to realize the tipping option's no longer easy to do post-purchase.
-- Matthew Hornbostel, game dev, game player, and maker of game assets: https://matthornb.itch.io/