Maria Hill was integral to the connection of the Avengers to broader world security. When she left, in the time between Age of Ultron and Civil War, her absence and the loss of her pragmatism resulted in World Security continuing to run on automatic for a bit but the wheels eventually falling off.
(I waver between her absence being due to personal illness, Fury made demands of her time, or the Avengers simply didn't bother to keep the relationship going, thinking they could do it themselves. Or possibly a combination of all three factors.)
(I waver between her absence being due to personal illness, Fury made demands of her time, or the Avengers simply didn't bother to keep the relationship going, thinking they could do it themselves. Or possibly a combination of all three factors.)