However, iPhone OS 1.0 launched without encryption enabled (not sure why, iPhone OS 1.1 enabled it), so this made reverse engineering efforts a lot more straight forward. For end-users, jailbreaking was trivial, you'd literally visit jailbreakme.com and a TIFF exploit in Mobile Safari would automatically jailbreak your phone (or in my case, iPod Touch) and install Installer.app[3].
A reverse engineered SDK was used to write apps and made quite the splash. This encouraged Apple to make available an official SDK. I'm not sure whether it was public pressure, or just that Apple saw the ingenuity of what people were achieving with Apple devices. However, iPhone OS 2.0 introduced the App Store, and the rest is history.
[1] https://www.theguardian.com/technology/appsblog/2011/oct/24/... [2] https://9to5mac.com/2011/10/21/jobs-original-vision-for-the-... [3] https://en.wikipedia.org/wiki/JailbreakMe