The GE90-110/115 was the first engine to feature swept fan blades.
But the GP700 and Trent 900 followed
And then smaller engines like the GEnX and Trent 1000
And then even smaller with the PW1000 and GE's LEAP.
So what is the advantage? Why didn't they exist before? Why does GE's LEAP fan look so different from the others?