IE was never W3C Standards compliant
This was only part of the problem. The bigger issue was that companies, governments, universities and their sites (the vast majority of them
) didn't stand up to Microsoft and insist Microsoft adhere to "industry" standards. So instead, Microsoft created their own standards and expected everyone else comply with them. And they did.
That worked back in the day when Microsoft ruled the world. And it might still be fine today had Microsoft been allowed (by Congress and the EU) to include AV code in XP like they wanted to. But MS was forced to remove the AV code (or risk forced break up, Ma Bell style). Then the bad guys moved in, in-part because of the totally unexpected (by all) explosion of "broadband to the home". But also because Norton, McAfee and the others failed to stop them after whining and crying to Congress and the EU that it was their job to stop them. Then the alternative W3C - more or less - compliant browsers started eating away at IE's dominance - much due to the exaggerated or even totally false claims about IE's lack of security (but that's for a different discussion).
So fast forward a few years and Microsoft changes its policies and philosophies and decides "security first" and "industry standards compliance" makes for better PR. So along comes the free MSE, then Windows Defender and now Edge, tossing IE to the wayside.
What needs to happen now is people need to let IE go. And that's hard, I know. IE was my preferred browser ever since Northrop Grumman IT (the company I worked for) threated to fire me if I didn't give up Netscape and move to IE6. I only switched to Pale Moon after the first Edge came out and IE started giving me problems. I'm convinced MS started sabotaging IE to force users to Edge - but that may be tinfoil hat stuff. But then I started having rendering problems with PM about the same time the new Chromium Edge came out so I switch to it, and liked it.
Now I'm used to the new Edge so that's what I use.
Part of the problem now is, IMO, companies like
Malwarebytes who continue to support XP (and thus IE) "enabling" those legacy users to keep using them. IMO, security companies like Malwarebytes should be encouraging their users to upgrade to modern, secure operating systems, not hanging on to obsolete, superseded (several times over), unsupported, insecure, legacy products. But that too is for a different discussion.