Hazlewood, who partnered left-arm quicks Mitchell Starc and Mitchell Johnson during Australia's 2015 World Cup triumph, expressed his frustration last week at first missing out on a place in the initial squad for England and then being overlooked as Jhye Richardson's replacement.
Richardson, ruled out with a shoulder injury, was replaced by namesake Kane Richardson, with Starc, Pat Cummins and Nathan Coulter-Nile the other pace bowlers picked.
"He just hasn't been playing any cricket," Langer said in England of the 28-year-old Hazlewood, who has claimed 72 wickets in 44 ODI matches.
"He's come off a second stress fracture in his back and while he's just starting to get up and running in the nets now - I think he's played six white ball games in the last 18 months - that's T20 and one-day cricket.
"We know he's a great bowler. He's a brilliant bowler, but it was just such bad timing for him."
World champions Australia head into the tournament on the back of an eight-match winning streak, including series wins away to Pakistan and India.
Much of the focus on Aaron Finch's team will follow former captain Steve Smith and David Warner, who are back in the squad after serving 12-month bans for ball-tampering.
Both played key roles in the 2015 tournament and have made plenty of runs in the leadup to England, with Warner top scoring in the Indian Premier League and Smith smashing two half-centuries off an understrength New Zealand in an unofficial warmup series in Brisbane.
Langer said both players were champing at the bit.
"It's been hilarious for me, because whether on the Anzac Cove or in the lunch room or we're on the bus playing cards, (Smith's) just shadow batting the whole time," he said.
"He loves batting -- he's shadow batting on the sand, he's shadow batting in the shower -- I'm not joking.
"They've (Smith and Warner) had 12 months to have a good think about a mistake they and the team made. I'm sure they'll be better people for that."
Australia play their World Cup opener against Pakistan in Bristol on June 1. The tournament starts on May 30.
(Reporting by Ian Ransom in Melbourne; Editing by Greg Stutchbury)
