Because I like OODA loops. It adds an interesting dimension to the combat. Players enjoy it too.
https://en.wikipedia.org/wiki/OODA_loop
Yes, this is the important part in bold. As for "simultaneous" vs "concurrent" vs some other term--that's just semantics. Who cares what word you use to describe it? The important part that combat is no longer an IGO-UGO; it's WE-GO, just like everything else in D&D outside of combat.
Ref:
https://en.wikipedia.org/wiki/Turns,_rounds_and_time-keeping_systems_in_games
Interesting, although I think you still get that naturally when people have to think and react more quickly without a fixed order of turns. I'm not saying it's really a problem, and some people will work better with a structure in place. I just prefer to not have a pre-defined structure. Each group of players seems to work out what works for them in the games I run.
It's not the word simultaneous that I think is confusing people, it's pairing it with initiative. The system we're talking about isn't simultaneous initiative, at least the way it relates to the normal D&D combat structure. It's no initiative - tell me what you plan to do and it happens when it makes sense.
Unlike other solutions, such as popcorn initiative, I'm not trying to redesign initiative as a game construct. All of those systems are designed to organize everybody's turns sequentially. The point, for me, is to eliminate that. Combat is chaotic, and everything doesn't necessarily happen simultaneously, but it's also not organized turn by turn.
Initiative is a system that organizes when a creature gets to start their turn. Because of the way it slices the round up, the normal initiative system also determines which creature resolves their action first.
The Initiative Check approach focuses only on which action resolves first. And then only when it's
necessary to know which action resolves first.
My goals are:
To erase the line between non-combat and combat. Or, to stop dividing the game into combat and non-combat. It often artificially limits the options of the players, whether consciously or not, to think that combat is the only option, or the "right" option once initiative is called for.
To erase the stop/start nature of slicing the round into individual turns. This becomes more absurd when there are more creatures involved because the round is still 6-seconds long. If there are two creatures, each turn takes 3 seconds. If there are 6, then each turn is 1 second. There are folks that will tell me that it's not start/stop, that when you describe the action it all flows. But the way the rules interact, that's just not the case.
"I move to attack the orc on my left."
"I move to attack the same orc, because I can use my sneak attack against it since my ally is already attacking him"
The orc is killed.
Why did the orc just stand there and allow the two creatures to move 30 feet and then attack? Wouldn't it have attempted to avoid them?
To better balance the activity timing among creatures. Being able to potentially complete a bonus action, action, another action (if you're a fighter with action surge), and move before somebody else does something in the round seems a bit much (to me).
So I think that using a term such as Simultaneous Initiative isn't really appropriate, because it doesn't describe the purpose appropriately, and may confuse the issue. I would just say 'eliminate initiative.'