Somewhere between the first Avengers and CATWS, Hydra starts the process of turning Steve into another soldier. Everything he does is monitored and most of the people he comes into contact with are Hydra. Maybe they moved him to DC because he was starting to make friends and they wanted to keep him as isolated as possible. Maybe he's so lonely and desperate for approval that he starts clinging to the members of the Strike team, who act friendly but them make subtle jabs and gaslighty comments that make him second-guess everything.

So basically Steve slowly losing himself to Hydra and not even realizing it, to the point where he's willing to do anything to get his teammates' approval. Maybe Brock or someone else in charge basically becomes his handler, and he starts obeying them without question because it's the only thing he can do anymore.

Extra moldy tacos if this results in Steve getting passed around like a party favor and convincing himself that it's fine because he's just helping his teammates.