Really? They just came from a war elsewhere. Standing up from XML trenches and walking joyfully into green JSON fields. JSON to hydrate UI's.
I don't remember that era of great UI. Sites were still inaccessible except no one cared, multitude of dark patterns still exists, confusing design language, no information organization at all.
The "trial-and-error" approach was much more "error-and-error" based entirely on guesses by the designer or engineer. I'm an engineer and remember, working through that time period, the horrible sites we created. I had a part in implementing them.
Not to mention the idea of "Web Application" was still very much incipiente in the mid-to-late 2000s. Who had great design for that? Go back and look at Youtube, Facebook, Twitter, MySpace back then, hardly a great example to be had, regardless of how bad we might think it is today.
The computing world was at peace until then, we had UI designers and engineers who through much research and trial-and-error produced very nice UIs for us to use. The UX industry came in and destroyed all that for shits and profits; literal decades of experience and precedence thrown out the window in the name of the latest fashion trend.