Back in August, directors Anthony and Joe Russo, who oversaw Civil War and will do so again with Infinity War, admitted as much, telling the Huffington Post, “I think him dropping that shield is him letting go of that identity.
[It’s] him admitting that certainly the identity of Captain America was in conflict with the very personal choice that he was making.”
The reason why people are convinced that we’ll see a new Captain America at some point in the near future of the MCU is that after his fight with Iron Man at the end of Civil War, Steve Rogers decided to leave behind his shield as he believed that he was no longer deserving of it.