Since Earth is extremely bright in the darkness of space, EPIC has to take very short exposure images (20-100 milliseconds). The much fainter stars are not visible in the background as a result of the short exposure times.
You know, if I'd been asked to predict any stated caveats they'd make with regards to this...project, "no stars" would've been right up there.
Along with mystically-poor fundamental resolution, represented here as being 15km.