[sp332]

That's an argument for an optional timeout, but it doesn't explain having a mandatory one.

[vbl]

Mandatory timeout means that even the best photos go away. No proliferation of the beautiful and perfect, no buildup of the quick and dirty.

Every one dies.

[alariccole]

True. I suppose the answer is that it was not the goal of the app to be in the photo storage/memories business. Looking at ways to help with this use case though, such as letting you save your own images to your camera roll.