No particular reason is when it's deleted as something like "Not Approved for 3 days", like my first one was (I don't know when it got undeleted though).
We don't delete for bad tagging, though it can make it harder to get approved.

In any case, practice more and turn up JPEG compression to 95-99% quality or switch to PNG. (I recognise it but I don't recall killing any shana of late)