The Gunners finished in fourth place after spending 128 days at the top of the league, and the Frenchman believes that a lack of maturity cost them dearly.
"We were on top for a good half of the season and then we cracked," he told French newspaper Midi-Libre.
"I believe we lacked maturity and that we had a lot of injuries at an important time. Above all we weren't able to adapt to the big teams.
"We have to show progress in these matches, to maybe play less football, but it's difficult because it's our playing philosophy."
Giroud, who has two years remaining on his current Arsenal contract, is in negotiations to extend his stay at the Emirates Stadium.