Social loafing

In social psychology, social loafing is the phenomenon of a person exerting less effort to achieve a goal when they work in a group than when they work alone.^[1][2] This is seen as one of the main reasons groups are sometimes less productive than the combined performance of their members working as individuals, but should be distinguished from the accidental coordination problems that groups sometimes experience.

https://en.wikipedia.org/wiki/Social_loafing