Why do you think so many college professors are so gung ho about group projects?

Of the four classes I am taking this semester, three have required group projects. I would say this is about the average I’ve experienced every semester since returning to college a couple of years ago. What drives professors to assign these projects? My informal polling shows that 90% of students hate them, believe they learn nothing extraordinary from them and consider them a huge waste of time and an even bigger pain in the hind quarters. So what’s the deal, why do professors seem to see them as a necessity?