You don't find smaller fish paying to power down significantly for a very good reason – they need to use their funds. They are earning the token in order to leverage it, to turn it into something else – something usable. They are not investing those funds in order to vote more things up because they recognize their votes mean absolutely nothing in terms of value to others or themselves, so there's no significant benefit to powering up, they end up holding a lot of liquid STEEM/SBD, and then they either decide that they can sell it for another cryptocurrency they can buy something with or they hold it just as long as it takes for the perceived value to be worth selling off for something else.

Note that they can't do that second part and power up. It is directly antithetical to using the token to lock it in a box and keep you from using it.

In effect, the 13 week power down trickle is most devastating to the smaller holder. It provides them good reason to not invest in the platform, to not make use of what tiny amount of power their given, and keep themselves free to actually use token for trade.

The guy holding 2 million STEEM isn't earning a notable amount, percentagewise, from writing posts and posting pictures on the blockchain. He's a speculator. He may or may not even have an idea of what "value to a social media based blockchain" actually means. By observation, he probably doesn't, nor should he.

Effectively, a 13 week power down simply centralizes more power in the hands of whales and gives anyone smaller good reason not to invest and not to be involved. Which, not to put too fine a point on it, fits with the rest of the design.