Forgive my ignorance, but why does SnapChat maintain a local cache beyond the 10-sec limit in the first place? Why don't they delete the photo and overwrite the

Forgive my ignorance, but why does SnapChat maintain a local cache beyond the 10-sec limit in the first place? Why don't they delete the photo and overwrite the disk space so that the photo is pretty much unrecoverable? Is it simply that this is too cumbersome to implement? Are there any technical restrictions? I tried Googling the issue and just came across the wave of articles that covered the discovery of the fact that photos were locally recoverable, but I don't seem to have found anything that indicates what motivated this design choice in the first place. Would be great if someone can shed light on this. PS: I'm not a SnapChat user, so I admit that I might also be overlooking some functionality of the app that necessitates the use of a local cache