Granted, Pepper and Bucky didn't exactly share any direct scenes together, so it's not like Gwyneth Paltrow forgot an immediate co-star. And there are dozens of main characters in the MCU. Pepper spent most of her time across the films with Robert Downey Jr.'s Iron Man and Jon Favreau's Happy Hogan. If anything, Paltrow should also be asking Chris Pratt who he is and who he plays in the MCU. Maybe she went ahead and asked Sebastian Stan that very question after talking to Pratt. That would be hilarious.