One time a KOA this was the case. Since they don't gates and UA
operates large aircraft (763/772) to KOA, i wondered the same thing. But then when I was flying to SFO
, we had an older woman in a wheelchair, who was capable of walking but not up the stairs to the 763's door. So, they put her in her wheelchair and into a scissor truck (like a galley truck), but has a window and is empty, presumably for PAX and equipment. She was raised to door 1R.
Here's a pick I took from Jetphotos. You can sort of see the truck behind the wings