The West Indies' World Cup ended in the first round at Hobart, a far cry from winning the title in 2012 and 2016 and the latest disappointment for the once-powerful Caribbean side.
They similarly won only one match at last year's World Cup.
"We just didn't turn up today," Simmons said after the West Indies were thrashed by nine wickets by Ireland in a match they had to win to progress to the Super 12 stage.
Disciplined bowling restricted the West Indies to 146-5, with Gareth Delany taking a career-best 3-16, before the Irish romped to their target for the loss of just one wicket with 15 balls to spare.
"We started well with the bat, but we just didn't continue," added Simmons.
"I think when you sum it up, we were outplayed in all departments today. They bowled well. We batted well at the start but didn't carry on, and they just batted well and batted us out of the game."
The West Indies came into the tournament in Australia with a new-look team led by Nicholas Pooran after the likes of Chris Gayle, Dwayne Bravo and Kieron Pollard retired. Andre Russell was overlooked.
Reflecting on the West Indies's dramatic fall from the top, Simmons said: "We have the batsmen, the capabilities, we just haven't been putting it together.
"Our bowlers are showing up nine out of 10 times, but the batters haven't really shown up.
"We've got to go back and look at our structure and how we play the game and make sure that when we come to competitions and when we play in bilateral series we are ready and able to do what's necessary for each situation of the game."
