Having struggled for starts with the Gunners over the first half of the 2017-18 campaign, the exit doors at Emirates Stadium opened for the Frenchman during the winter transfer window.
Alexandre Lacazette had already nudged him down the pecking order in the eyes of Arsene Wenger, and Aubameyang was then acquired in a club-record £55 million deal.
Giroud concedes he was no longer prepared to fill back-up duties, with Wenger acknowledging that a top talent needed regular game time in order to fulfill a World Cup dream this summer.
He told France Football: “The coach immediately said to me: ‘Don’t worry, I will do my best so that you are happy’.
“On one side, it was normal. I had never asked to leave. On the other, I knew that he would not cause problems given the relationship we had always had.
“He [Wenger] even said to me that it would p*** him off if I did not go to Russia.”
Giroud added on his time in north London: “It was frustrating at Arsenal, obviously. For a year and a half, it went from bad to worse.
“I could no longer continue like that. I could not bring myself to spend another year at Arsenal and remain a reserve, even a second reserve.
“The future looked gloomy with the arrival of a new striker. I wanted to become happier again by playing, so I left – it is as simple as that.”
Giroud was initially lined up by Dortmund as a possible replacement for Aubameyang, but a delay in that move getting done, coupled with the birth of his third child, led to him staying in England while Michy Batshuayi headed out of Stamford Bridge to Germany.
“The easiest solution was to go to Dortmund,” added the 31-year-old frontman.
“Arsenal were happy, Dortmund as well. It was the offer most interesting financially speaking. I have a very good contract at Chelsea but Dortmund really wanted me.
“It happened after a game of poker, like in all transfers. It dragged on, I started to get stressed because my third child was born at that exact moment. That was also why I did not want to go to Dortmund.
“Spending four months without seeing him, I do not know how I could have done it. It was why I needed to take the bull by the horns.”