Kehrer won a number of trophies with Paris Saint-Germain, but last season made only 16 starts in Ligue 1 and was only given cameos when he made it off the bench later in the campaign.
He moved to West Ham in the summer and at the London Stadium, has played in every available match so far.
Kehrer explained that while he achieved many successes with the Parisians, he recognised it was time for a new challenge and West Ham appealed to him.
“I was in Paris for four years and had an extremely successful time there, winning many trophies”, Kehrer said in a press conference.
“It was time in the summer to take a new step and a new challenge.
“West Ham is a very interesting project.
“That felt the best for me.”
The centre-back had talks with Flick, with the World Cup in mind, and they helped persuade him to join West Ham.
“Of course we [the coach and myself] talked about what is important in this season, which is a special one with the World Cup in the middle of the season”, Kehrer added.
“He told me what he wanted from the players in general.
“After this conversation I thought about it and made the decision to go to West Ham.”
Kehrer has been called up to the Germany squad for the Nations League games over the international break and it remains to be seen if his decision to move to West Ham pays off with a World Cup call-up.
