Such was the case when Zemo, the newest villain in the MCU, appeared during Captain America: Civil War.
The following contains some spoilers for Captain America: Civil War.
Even if theyd tried, that would have been additional screen time taken up by Zemo, when the true focus of Captain America: Civil War was designed to be the heroes.
One of the key elements of Captain Americas history is that hes a soldier who ends up frozen during World War II.