I'm sure 5s's are fetching at least $400 on the conservative side. If all I have to do is spend like $5 and follow a how-to on a website, I think a lot of people would be willing to make the investment.
Keep in mind that if these criminals can't figure it out by googling it, they will give up and move on. The typical phone thief isn't a security expert with the knowledge to invent a previously unknown exploit.
I can think of some examples:
* jealous spouses who want to look at call logs, emails, text histories
* unscrupulous managers looking to see if you've been talking to headhunters, competitors, etc.
* stalker coworkers who are looking for "private selfies"
* frenemies who want to post inflammatory messages using one of your social media accounts