I wonder if they are discouraged by the experience of Con Kolivas[1] who proposed an alternative scheduler back in 2007. (Apparently he is still maintaining his "-ck" fork of the linux kernel[2]!)
I only mention this as a historical case that has remained in my memory. Maybe Linus is willing to revisit the issue, I don't follow LKML.
I do not follow Kernel Dev enough to have a good representation of what happened, but it seems to me that it was another example of smart people pushed out. Nowadays I think he is just maintaining his patches from one kernel release to the next, it was smart for Con to stop interacting with them and move to other types of devs, it comes a point where you have to keep your sanity.