You seem to think that the indexing and searching happens only if there is a reason. Why do you think that? There are all kinds of cases where government agents were found to have abused access to data for reasons that had nothing to do with illegal or immoral behavior by a target.
Irritatingly naive
Because they can.
So they randomly picked a person to search?
They have a jealous ex who is a LEO.
Never been across an international border?
Speaking of which, iOS needs to finally support user accounts, ideally hidden ones as well.