You’re allowed to change your mind without calling a press conference.

Changing your mind gets treated as something requiring justification, so people stay in plans they hate purely to avoid the explanation. You are not a public figure, though, and nobody is owed a statement. Quitting the team, dropping the class, ending the thing, most of these need one short sentence and nothing more.

Try the plain version: I thought about it and I am not doing it anymore. No history, no defense, no long thread in the group chat. A few people will ask why, and you can answer briefly or not at all, and the week goes on either way.