It has the advantage of allowing the iCloud team to update the preferences panel without the need to release macOS updates. Allowing them to decouple iCloud updates from the macOS release cycle.

Sure you could use something like SwiftUI and create some simple DSL to dynamically build a native UI. But at that point you’re basically building a slightly crappier, less flexible version of HTML. So might as well use HTML+CSS and take advantage of the decades of learnings it represents.

I’ve personally used a similar approach to power a banks fraud warning UI. Made it possible for us to quickly iterate and change our UI as various strategies used by fraudsters evolved. Meant we could go from see a new issue, to updating our ML models and deploying new UI in under a week, which is faster than the app review process.