I think it's because our prospects of importing even more deflation in the future keeps getting greater. The dollar should keep strengthening and that's going to make imported goods even cheaper.
The US, being the predominant economy, does not import inflation or deflation from anywhere. We create these things and we export them in some measure. So long as the Chinese economy is expanding, it is soaking up our excess dollars. When that economy hits a wall, as is likely soon to happen with the general insolvency of Chinese banks, China will not be importing our excess dollars anymore and we will be stuck with them and will experience a sharp rise in prices throughout our economy. It gives one a bit of a sour taste to think that keeping prices down (except for housing and oil) depends on keeping the main commie economie booming.