I'm guessing you missed the time period where opening the wrong page would give you an infinite loop of un-closeable pop-up windows with background music.
Ads were never really non-obtrusive. If advertisers could force you to listen to their slogan at max volume every time you opened your browser, they would do so without hesitation. If you ever saw an easily avoidable ad in the late 90s-early 00s, it wasn't for lack of trying. They simply hadn't personally figured out more annoying methods yet.