Back in the early days of the iPhone, jailbreaking was an incredibly common practice for enthusiast. With an iOS jailbreak and third-party app stores like Cydia, iPhone users were able to add software features and apps to their devices that Apple had yet to provide (sometimes years prior).

Two things happened those to shrink the jailbreak

Source: Hot Hardware – Unpatchable iOS Exploit Could Bring Permanent Jailbreak For Millions Of Devices Including iPhone X