It's not unreasonable to think that Easter eggs might be written to contain back doors. Certainly any large software project that has workflow gaps where unvetted code can be introduced is a recipe for disaster.
Why make the backdoor obvious by incorporating an easter egg when you could just make one that does not draw attention to itself? You can still make non-obvious backdoors with this policy in place.
An Easter egg containing a funny animation can be used to distract from the malformed image that serves as a back door that exploits a bug in the image renderer.
