The early years of the Marvel Cinematic Universe introduced unique ideas that seemed relegated to the movies they appeared in. For example, the Frost Giants didn't show up in live-action after the original Thor, while many other plot threads reappeared in future films. From the return of The Leader in Captain America: Brave New World to Red Skull reappearing in Avengers: Infinity War, there's a consistency in old ideas impacting the universe at some point in the future. Even still, one particular group of enemies from Iron Man 2 has failed to reappear in the MCU.
Source：https://www.cbr.com/where-are-mcu-hammer-drones/
