Antonio Conte led the Blues to the Premier League title in his first season in English football, Chelsea having failed to qualify for Europe after finishing 10th in the 2015-2016 campaign.
But with European commitments adding to its domestic duties, Chelsea has struggled to maintain its form from last season, sitting fourth in the Premier League after successive defeats against Bournemouth and Watford.
Chelsea was also beaten by Arsenal in the semi-final of the Carabao Cup last month, with Hazard citing extra games as a reason for Conte's side finding life harder this term.
"I think the Premier League is difficult," he told ESPN FC. "It's hard to win every year.
"Last year we didn't have the Champions League. This year we have less time to be ready for the games. Every week there are three games."
Chelsea is also without two of its key players from last season, Diego Costa having returned to Atletico Madrid and Nemanja Matic being sold to Manchester United, while club icon John Terry departed.
Costa's replacement Alvaro Morata has lost form and been unable to stay fit, while midfield signing Tiemoue Bakayoko has failed to adapt to the Premier League, the former Monaco man sent off in a 4-1 loss at Watford on Monday.
"We changed a couple of things, we lost players, we brought some new ones and every year is different," Hazard said.
"That's why we love football - if there is only one team that wins it would be boring. That's why football is special. You never know what's going to happen, especially in England."