Earnings have gone up quite a lot over the last 10 years and as the Shiller PE takes an average of the last 10 years earnings, it will mean it's using a lower average earnings than todays earnings for it calculation.

Combine that with todays prices not actually being very cheap, it's resulting in a high Shiller PE. As long as earnings remain the same (or increase) even if stock prices don't go up the Shiller PE will start to come down over the next few years.