One of the problems is the 12:15 outbound doesn't have any low fares available. The lowest available fare on the 12:15 nonstop is a B fare, which is almost full fare. The other non-stops have Q fares available. The 4PM non-stop has V fares available. Try the other outbound flights. It's surprising that the 12:15 outbound isn't offering any discounted fares on that day. The morning non-stop is usually the most popular outbound flight.
I don't know what your return date is, but if it's 12/23, I found a fare for under $800, returning on the redeye via LAX.
There are no S or T fares. Those are the cheap ones.
You have a Mileage Plus number, right? If you want to see the available fare classes on united.com, go to www.united.com
, logout if you're already logged in, then login on the right side of the page, selecting "shop for flights" in the pull-down box. You have to use "muti-segment" itinerary and diplay availability by "schedule". You also have to set your preference to "an expert" under profile/all preferences. (scroll down to "Display Preferences"/"Availability Format").
I usually check fares via SFO-LAX-OGG and SFO-HNL-OGG if I can't find anything decent on the nonstops. I'm sure you know that already.
You might want to hold out for S or T fares. Of course there's a risk if you wait. On the other hand, I hate the red-eye.