When IE was the Emperor it was seen as IE's behaviors
were the standards. The perspective at the time was that the other browsers were non-standard. That did get codified into the standards eventually. `* { box-sizing: border-box; }` that is towards the top of almost every "reset.css" is CSS standard for "use the IE box model". XHR was named XmlHttpRequest as an IE quirk and that set the standard we still mostly follow today; `fetch` is a nicer API but we still colloquially call it a part of/relative to/replacement for XHR including various browsers' Dev Tools where to focus on `fetch` requests you click the XHR tab.
Both of those things (and others) became "standards" when IE was moving quickly and breaking things. It took a while for the actual multi-browser standards to catch up. XHR took a few years to show up in non-IE browsers. CSS `box-sizing` wasn't added to the CSS standards until 2012 (11 years after IE6 was released, the "last" version of IE for a long time; five years without a new version). A lot of the web was built easier on those things or better with those things which lead to so many people using IE up to IE6 as their primary browser and so many developers building IE-only websites up to IE6.
Again, as a developer it can be easy to remember the pain of still supporting IE6 in 2005 (five years before tools like `box-sizing` made it a lot easier to support similar CSS for both IE and non-IE browsers, and a year before IE7 finally broke the "IE6 is the last IE" problem). It seems a lot harder to remember why we were still supporting a "dead"/"final" IE6 in 2005 or still supporting a "dead"/"final" IE6 in 2012 when IE10 was fresh and new and very standards compliant (including supporting both `box-sizing` modes) but not yet winning over the crowds of legacy sites: everyone was using IE6 until Microsoft killed it. A lot of things were built for its version of "standards" (many of which were better/easier to develop for versus their contemporary real standards) and couldn't be easily upgraded until the real standards also caught up to how fast IE had been innovating/changing/upgrading the standards.
The risk to the web platform that I think IE represents the most cautionary tale about is relying too much on the browser rushing ahead of the standards, because it could stop at any moment and may take a decade or more for the standards to truly catch back up. Because they did.
If Google decided today to do a "The Browser Company-style pivot" because the Age of AI means that browsers are dead, everything a browser can do should be done through agentic automation, and asked all of the Chrome team to switch to some new agentic harness or accept a soft layoff, how much work would there be to move websites out of being "Chrome-only" or built on top of Chromium? (Which to be further unfair is also sort of what feels like is already left of Microsoft's Edge team working in Chromium today.) It's real easy to imagine that hypothetical, I already named two companies working with Chromium that have just about done exactly that. The hypothetical is not that far from the inside baseball of what happened to IE6 where Microsoft thought browsers were "done" and pivoted the IE team to new roles on "higher priority" Windows work and/or soft layoffs.
We remember the pain of having to support older versions of IE pretty well, but not enough of us seem to remember the pain of how we got to that point and how easy it feels like companies could do that to the web again. Safari lagging current standards is a relatively smaller problem compared to if Chrome gets burnt we suffer another "internet dark age" of supporting ancient browsers for a decade or two due to legacy apps and in turn legacy users that don't or won't upgrade.
(Some would argue that can't happen in the same way that IE did because Chromium is open source and already has many forks. I can't help up but bring up examples like the word "diaspora" and the tale of "the Tower of Babel" that a messy soup of forks that no one can agree on as the new "standard" can be its own slow train wreck disaster.)