Belgium were without injured captain Eden Hazard, but De Bruyne created two great second-half chances which Lukaku and Thorgan Hazard came agonisingly close to converting.
"We're disappointed, but we have to be realistic -- we knew it would be difficult because many factors worked against us," De Bruyne told broadcaster RTBF.
The Manchester City star pointed to Eden Hazard's hamstring injury, Timothy Castagne's eye injury in the opening game and the fact Axel Witsel had only just recovered from injury before the tournament.
"We had too many problems to be at 100 per cent, personally, I wasn't 100 per cent," admitted De Bruyne, who overcame an ankle problem to play.
"I thank the medical staff who did an incredible job so that I could play despite a torn ligament.
"I fought hard, we all fought until the end. In the first half, Italy were better, but we had chances to make it 2-2.”
"Some people will be disappointed and will criticise us but I think the fans saw that we gave everything."
De Bruyne said the Red Devils will "try again" at the 2022 World Cup, but goalkeeper Thibaut Courtois admitted the quarter-final defeat "hits hard".
"We had two opportunities, but their keeper made a good save and I think we gave the first goal away a bit too easily," he said after Barella beat two defenders to break the deadlock.
"It really could have gone either way, but Italy deserved to win here."
Defeat means more Euro quarter-final heartbreak for Belgium, who exited at the same stage in 2016 after defeat by Wales.
"It's sad and disappointing, these players don't deserve to go out," said Belgium coach Roberto Martinez.
"I can't fault my team, they were magnificent."