I believe Deku's popularity in his hero costume clothing from his innate heroism and strong sense of justice, not just from being the protagonist. Wearing a Deku gym shirt during workouts enhances their significance.
He wants to express his gratitude to his teacher, the legendary Hero All Might, for giving him personal attention. Additionally, he wishes to thank his classmates from Class 1-A at U.A. High School, particularly his partners Katsuki Bakugo, Shoto Todoroki, Eijiro Kirishima, and Tenya Iida, for their support, trust, and positive influence.
