I guess this is something that we will never know for sure. Call of Combat was a good name, intrinsically. But for many people the association with a famous FPS franchise was unavoidable, and as such made the game feel like an opportunistic rip off for probably too many people.
That was confirmed after the Kickstarter, we did talk to some people in the video game industry, publishers and investors. A few of them that implied or explicitly advised to consider a name change from Call of Combat. There were also forums, subreddits and such where the name "Call of Combat" was actively criticized and mocked, for sounding unoriginal and opportunistic. We felt this could be a serious obstacle to the success of the project.
It was very obviously a difficult decision, but, now we think it was a good one, people's reaction to Divided We Fall has been usually much better than to Call of Combat. The Steam Early Access had a much much bigger reach than the Kickstarter and we have not seen even a fraction of the criticism we've seen for the name "Call of Combat".