> but isn't it a lot of code and testing to implement the personalization UI? But thinking about it more, I suppose the answer is to let the users write their

> but isn't it a lot of code and testing to implement the personalization UI? But thinking about it more, I suppose the answer is to let the users write their own clients. That's certainly one reason (on the operational layer), but I very much doubt it's the main reason. Otherwise, companies wouldn't go out of their way to prevent you from writing your own client. My suspicion is, there is an additional layer between data gathering and customisation that is extremely interesting for companies: the target metric. If you're allowed to customize things yourself, you supply your own target metric to judge if the current settings work well for you. It's mostly implicit, but I'd guess in most cases, it would be about ergonomics, how easy you can archieve things that are important to you, how much it matches your personal visual style, etc. Telemetry and "forced personalisation" allow the company to supply their own target metric instead. Yes, ergonomics and personal preferences play a role, but the company can easily mix in other things, such as retention, which are exclusively important for them but not for you.