What circumstances discourage low wage workers from seeking out and taking the best paying job that they can find?

From the text:

Why didn't they just leave for a better-paying job, as I did when I moved from the Hearthside to Jerry's? Part of the answer is that actual humans experience a little more "friction" than marbles do, and the poorer they are, the more constrained their mobility usually is. Low-wage people who don't have cars are often dependent on a relative who is willing to drop them off and pick them up again each day, sometimes on a route that includes the babysitter's house or the child care center. Change your place of work and you may be confronted with an impossible topographical problem to solve, or at least a reluctant driver to persuade. Some of my coworkers, in Minneapolis as well as Key West, rode bikes to work, and this clearly limited their geographical range. For those who do possess cars, there is still the problem of gas prices, not to mention the general hassle, which is of course far more onerous for the carless, of getting around to fill out applications, to be interviewed, to take drug tests. I have mentioned, too, the general reluctance to exchange the devil you know for one that you don't know, even when the latter is tempting you with a better wage-benefit package. At each new job, you have to start all over, clueless and friendless.