I know MS put the kibosh on most easter eggs after some "trustworthy software" initiative in the early 2000s, which I think was to assuage government concerns that they could also be sneaking malicious backdoors into their software (silly reasoning), or that there could be vulnerabilities caused by an easter egg (ehhh...maybe).
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.
