Legacy.<p>For a long time IE could be depended on to either a) not support a standard b) claim to support a standard but do it wrong or differently from anyone else or c) have equivalent behavior to a standard but with proprietary extensions.<p>Also, Microsoft bundled IE with Windows to leverage its desktop monopoly power. <a href="https://en.wikipedia.org/wiki/History_of_Internet_Explorer#United_States_v._Microsoft" rel="nofollow">https://en.wikipedia.org/wiki/History_of_Internet_Explorer#U...</a>
Originally, mostly for ideological reasons and because people simply followed the anti-Microsoft trend. Technologically, IE was not a bad browser when it was released and had quite a few advantages over Navigator/Communicator.<p>Of course, when Microsoft decided to abandon the whole thing and the competition (i.e. Mozilla) continued working on it, IE slowly lost these advantages.<p>So, down the line there were certainly also technological reasons why people were not too fond of it, but most of the dislike originated from said anti-Microsoft ideology. Of course, we are speaking here about 20ish years ago.
The business model of IE was such that it was propped up by Microsoft alone. Due to poor leadership at Microsoft this was not viable and it was surpassed by chrome and Firefox. People hated IE because it fell behind, and Microsoft kept pushing it long after its expiration date.
Performance. Firefox’s angle against IE was privacy, and it attracted a lot of techies. When Chrome came out it won the game with superior browsing speed