why did he say no?
Granted that this movie has a ton of plot holes. There is one I can't think of even a good explanation for. In the beginning, they show a flashback of Frank saying he wouldn't take the job and referring it to the other transporter. Later on he knows nothing at all about what's going on.
Why did he say no to begin with then? They would've had to have told him something about it for him to turn it down.