Surprised that Ars didn't jump to the most obvious conclusion: a legal compliance issue.
Presumably, five or six years ago, someone from the DOJ or FBI told Facebook it would be really handy if they stored user images indefinitely, and Facebook, not being a company that insists on seeing warrants or subpoenas, said "Sure, why not."
Presumably, five or six years ago, someone from the DOJ or FBI told Facebook it would be really handy if they stored user images indefinitely, and Facebook, not being a company that insists on seeing warrants or subpoenas, said "Sure, why not."