It happened because short-sighted and sloppy authors failed to use progressive enhancement over a pure HTML version that worked on every browser ever to exist.

It happened because short-sighted and sloppy authors failed to use progressive enhancement over a pure HTML version that worked on every browser ever to exist. Instead they picked one browser they liked, wrote bogus code that happened to work on it, and declared "if you aren't running what I'm running, fuck you". In five or ten years we're going to be hearing the same kind of whining about how the Chrome and Firefox holdouts are holding back Web 5.0, blaming user agents when it's their own bad authoring at fault.