Everyone has a back story, and we, the audience who just came here to see Sly battle the forces of the tunnel, are supposed to watch, learn, and care about them. Let 'em die. They're the fodder, the bait for getting Sly to jump through the hurdles. And are treated as such, to the movie's credit. See, all good disaster flicks need follow a certain pattern.
Disaster strikes a bunch of innocents.
About 10-15 survivors fight their way to freedom. About 8-10 make it out. Which means the film has got to be able to kill off some good guys. And it does. It's the only way to make it remotely believable.