A big problem with purchasing Steem Power is that it is extremely difficult to liquidate once you power up. If you ever decide to Power down and sell your Steem Power you can only do it over the course of 104 weeks (2 years) in 104 equal installments. Steem Dollars and Steem can be sold at any time. Yes, there is a strong incentive to Power Up but only if you are totally convinced in the longevity of the Steem project. Whatever Steem Power you now have cannot be fully sold or liquidated for a full 2 years. 2 years is an eternity in the blockchain space, many things can happen.
Lets take all scenarios into consideration and not just blindly hope for the best. Many of the whales are cashing in their Steem Dollars on Exchanges rather than powering up.
That being said, if you firmly believe that Steem will be a great success (which I do) by all means Power up all your earnings and collect that high interest rate that the platform pays.
I think the slow power down is the system's strength, if market confidence ever plummet, there's still time for the community to come together and solve problems, regaining market confidence.
It certainly is a fundamental design pillar but perhaps 2 years is somewhat excessive.