[berkes]

There were many websites that used just HTML, CSS and some JS and none of the "proprietary VBScript or ActiveX (or Flash)" that would not work on anything except IE6.

Most competing browsers chose to implement IE6 rendering (border box model, quirksmode etc), bug-by-bug. To at least have some of those "built for ie6 only" websites functioning and looking OKish.

But when those quirks would break the website on anything but IE6, many webmasters (is that still a function-title in 2021?) would not care, or not get budget to fix it: "96% of our users use IE6, why spend time for those 4%?". (which also begs the question: what are those 4% doing on a website that doesn't work at all for them? Shouldn't that be 100%/0%)