This post is focusing on when whales upvote, in general, relative to a post's publication time. It's almost impossible with this data to say why the whales vote in this way. Since there's no curation penalty after 30 minutes, it makes sense that most whales vote at this point. You could ask that since whales have already made it, why aren't they more altruistic, sacrificing their own curation reward for others?
I don't think posts should be rewarded after 4 weeks because that's probably not good for the steemit economy. Don't ask me why, it's just a feeling. I agree that the reblog feature will help get posts "out there", and it emphasizes the importance of building a good following rather than trying to "get rich quick".
I realise we can't deduce intention from this data. Thanks for doing this anyway. More data is always a good thing and I'm sure people will draw their own conclusions. Cheers