I think the purpose of both routes is to give OAK and PHX additional westbound frequency, to offer travelers more flexibility. But at the same time, red eyes would not fill up....although they would do great in LAS and RNO. I think both flights feed red-eyes.
And also there are lots of through passengers going ATL-PHX-LAS...the plane was more than half full when I flew PHX-LAS on DL and there were very few local boardings in PHX. (I used that segment to get a $250 one way PHX-SYR fare...routed myself PHX-LAS-DFW-MCO-SYR, using PHX-LAS, LAS-MCO, and MCO-SYR fares.)