As is typical of commuter crews, the Skywest pilots probably had a lot of work to do in a short period of time and to keep things rolling, they asked for an intersection takeoff. Probably all that remained was to taxi into position, perform whatever line-up checks required by the company and await takeoff clearance. So far so good. At a busy place like LAX, there's constant activity and most of it will be described in some fashion by radio calls between aircraft and tower and ground positions. If you're on the tower freq, listen for landing and takeoff clearances.
Some pilots make a habit of listening to tower on one radio, ground on the other.
In a perfect world, the Skywest crew would have made a mental note of this and maybe even discussed the fact that an airplane was about to land on the runway they would soon depart from. Evidently, they did not. Forty five seconds later, the Metroliner was still in position on the runway, the downfield traffic had long since cleared. The USAir Boeing again called, now well inside the marker. In just short of a minute, it would have eaten up close to half the distance from the marker to the runway threshold.