Why did James Gunn not reveal Mantis and Peter Quill's relationship in "Guardians of the Galaxy Vol. 2"? That's anyone's guess but in a chat with TVLine, Pom Klementieff said, "Gunn decided to hold onto it, and reveal it later." Seeing as it's such a pivotal bombshell that adds layers to Peter's character, it makes sense why Gunn thought it was best to wait for the reveal to have its own moment. Dropping the news in "GOTG Vol. 2" would have left it as a major cliffhanger for nearly five years.
Beyond that, audiences would have likely expressed their frustration for years, as the Guardians had small appearances in "Infinity War," "Endgame, and "Thor: Love and Thunder" following the release of "Vol. 2." With the "Holiday Special," Peter and Mantis' relationship was given the perfect time to shine, which makes it all the more special. Besides, Mantis' character in the special spends most of the time fearing Peter's response — a character choice that likely wouldn't have paid off in any other Guardians appearance. Continuing her chat with TVLine, Klementieff expressed how she's pleased fans know the truth because "it creates more layers and a special and beautiful, bond between the two characters."
