Every elevator has a capacity sign. Pack too many people in and nobody goes anywhere. Teams are like that.

Adding people to a job past a certain point starts making it slower. Beyond the limit everybody is coordinating instead of working, nobody knows which part is theirs, and the whole thing stalls while looking busy, which is how a five-person group project produces less than two people would. More hands are not automatically more progress.

In your next group task, break the work into named pieces and say out loud who has which. Keep your own piece small and finished rather than large and vague. If the group is too big, suggest working in pairs instead of all together.