Why a configuration option is in a registry key and not in the interface?

My job at Veeam is the first time in my IT career working in a software company, and I’ve learned a ton of things about software development. Not as a developer myself, since I don’t have any code writing skill (I wouldn’t call my low scripting capabilities “coding”), but partecipating to internal discussions about development has been so far an interesting experience. One of the most fascinating things I’ve learned is UX (User Experience) development, in particular around the User Interface.