Bagpuss
Legend
I've been playng RPG's now for about 30 years off and on. One of the things that used to annoy me was the unrealistic turn based initiative systems, and everyone uses them.
Well not everyone...
Feng Shui and others have been mentioned that use a sort of seconds (or shots) based initiative, where actions take a set amount of time and you can't act again until that time is over, so if you take a short action you can act sooner than if you take a longer one.
Then there are others that have actions happening simultaneously, so attacks are declared and damage calculated but it isn't applied until the end of the round, so the guy you might kill in a round still has a chance to injure you.
Then there are games that just work on the whole scene as one event, rather than turn by turn so again everything is simultaneously.
Then there are others that initiative is passed based on the narrative (Marvel Heroes) and not a dice roll.
So I wouldn't say everyone uses turn based initiative, the reason it is so popular is it is a simple abstraction, that works well most of the time and one people are use to.