In many different areas UA is middle of the pack and in many areas customers care about, the differences would have reflected poorly on UA --

E+ --- lot's of airlines have - not really a factor that sets UA apart anymore
Wifi --- lot's of airlines have - many have significant advantages
MP --- certainly better than some, but increasingly nothing to shout about
Lounges -- ok, next question
Planes --- fleet overall is probably no worse or better than other domestics, but the cabins are not maintained at the same level as JL, CX, SQ, EY, LX, LH
Food -- ok, stop laughing
Wine -- please stop laughing
Limes - are they back
Split Cashews - customers prefer them
J Seats - two distinct types -- neither are market leading offerings
F Seats - maybe one of the poorest among airlines that offer F
Fares - no advantages/disadvantages
On-Time/Ops -- not sure you want to bring that up in a UA ad

At least with network - for the person that wants one airline to go lots of place, UA has a good story -- and I suppose that's why they are focusing on it --