So with the other individual movies (Thor, Iron Man, The first two Cap' films), individual avengers may play cameos of supporting rolls. In the avengers films, it has been a collaborative effort with no individual getting a significantly larger amount of screen time than the others.

In Civil war, Tony stark gets at least as much screen time as Steve Rogers, and some of the others (Natasha Romanoff, Vision, Wanda Maximoff) come pretty close to getting a "co-star" level of screen time as opposed to "supporting cast".

Given all of that, what executive and marketing decisions lead to Civil War being billed a Captain America movie?