When I went to college, I had a computer science professor who assigned a group project, and he also told us exactly how to do a group project. You know, how to organize it, how to distribute work, how to have meetings and report progress, etc.
That was the first time any teacher had ever explained anything to me about the group itself. The professor thought it was a good way of introducing students to the way things are done in a workplace, and he was right. Group projects are hard. If the students have to figure it out themselves, they will screw it up royally, just like anybody would.
I honestly believe that every teacher I had up until that point had no interest in using group projects to actually educate the students. It was just a break so that the teacher could pretend like they were teaching students to work in a group, but actually added little scholastic value for students. (There was some inherent value in the socialization aspects, but the teacher never told us to do that, either.)
If teachers don't teach, then it's only luck if students end up learning.