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.
Also, Microsoft bundled IE with Windows to leverage its desktop monopoly power. https://en.wikipedia.org/wiki/History_of_Internet_Explorer#U...
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.
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.