No, proper easter eggs don't introduce security issues, they're benign almost by definition. I think what made them disappear was the introduction of all the suit-wearing people who decide what the programmers are supposed to program, with no room for autonomous work within that.
> proper easter eggs don't introduce security issues
Proper code doesn't either, and yet there they are! The point is they added another attack surface, however small, and another code path that should be tested.
When people started to care about 100% test coverage, they started to disappear.