One thing about motorcycling is that you tend to end up where you look, and a lot of people crash into oncoming traffic in corners because the focus on the oncoming car and not on getting around the corner.

I get the feeling that this guy tried to veer, and then refocued with all his attention on the truck that was getting closer and closer, and that made it quite impossible for him to evade. He could have saved it by doing a million things, but large and threatening objects that are approaching usually demand our attention. Silly, primeval behavior.

Looks like he instinctively tried to veer left, since the truck was moving right, but then the truck started moving back left and that confused him to stop his veer to the left and then... Crash.

If he and the truck had moved opposite directions it would have gone better.

This looks like an unfortunate case of target fixation. You tend to move toward where you look and he was looking at the giant truck heading toward him.

Edit: Target fixation can also help you predict how other drivers are going to move. A driver who wants to change lanes will often veer slightly toward that lane as they check their mirror and blind spot. A second later you will see them turn on their blinker (or not if drivers around you suck) and then shift lanes.