I still to this day do not understand why the UI designs of yesteryear had to be replaced with "dynamic" javascript bullshit, infinity scrolling, having every element pull data from AJAX calls after page load instead of just serving it in the initial request etc. Modern UIs fucking suck because they violate your expectations. You click "see more" on a comment, or you click the replies, and instead of seeing more, the whole thread just disappears because it wasn't kosher according to the algorithm. I know you know what I'm talking about.
Or how about when they replaced their straightforward subscription system with that stupid bullcrap where you have to "hit the notification bell" to continue seeing the content you subscribed to? And even that doesn't work some of the time.
Old UIs were simple, straightforward, and just did what you expected them to, without layers and layers of spyware, censorship, and shadowbanning BS built into it