Giroud fell down the pecking order following the signing of Alexandre Lacazette last summer.
The striker also revealed that with the arrival of Pierre-Emerick Aubameyang, it would have reduced his playing time at the Emirates if he stayed with them.
Giroud has now moved to Chelsea and admitted that he was unhappy with the events that led to his move away from his club.
“The fact is that the coach wanted to recruit a new striker and with Aubameyang’s signing at Arsenal, there were three top strikers, and that’s why I decided to leave,’ the 31-year-old said.
“It made sense for me to take a new direction in my career.
“There was a bit of disappointment, even though I spent five wonderful years there.
“I could have stayed, but I needed a solution to get back in.
“I wanted to stay in the Premier League and Chelsea was a great opportunity for me.”