It's not only ORD/LAS. ORD/RSW had been between $550 and $625 RT in first for a long time (P fare), but suddenly jumped to $925-$1,200 last week and has stayed there. Meanwhile, UA is still in the low $600s nonstop and if you don't mind a stop in ATL, DL is around $450.
I thought that it was a quirk that would work itself out in a week, but maybe not. UA now gets my business until AA comes to their senses. I make this run about a dozen times a year, so the difference adds up fast. The recent destruction of C inventory has made matters much worse, so P fare costs are far more important than they used to be. I know that it is AA's plan to eliminate C opportunities to force some flyers to buy P fares to guarantee being in front, but that only works if AA's P fares are competitive. On this route, they are not so the plan backfires. I am sure there are many more routes like this.