Bingo. Lack of awareness of what other people are doing. Self-absorption, obliviousness, inattentiveness, and in many cases, plain old ignorance.
Of course, this quality manifests itself in a lot of different kinds of pedestrian behaviour - stopping suddenly, text-walking, a group of people having a conversation in the middle of a busy sidewalk, and the like. It would be reasonable to say that the guilty parties in the above scenarios all either lack a basic sense of situational awareness, or they're simply jerks who don't care if their actions negatively affect others.
Looking at it from this angle, the relationship between slow walking and career success becomes immediately clear. Situational awareness is a crucial interpersonal skill, and if you're constantly doing things at work that annoy the hell out of your coworkers, you're probably not going to last very long.
You might be thinking, "well that's silly! I can walk as slow as I want in my free time, but that doesn't have any relationship to how I behave around others at work!"
Are you so sure? There's a funny thing about insight, and it's that we don't know what we don't know. Couldn't it be possible that that same quality that's responsible for you inducing silent rage in dozens of anonymous pedestrians is having some other effect on your behaviour in other parts of your life?
When it comes to insight, there's four possible states for a person to be in. There are things that you know about yourself, and other people also know (like your fashion sense/lack thereof). There are things that you know and other people don't know (such as your undying love of classic Michael Bolton songs). There are things that neither you nor anyone else knows about you (the unconscious... scary). Finally, there are things that you don't know about yourself, but others can see them as plain as day. Slow walking, or any other behaviour inspired by a lack of situational awareness, falls into this latter quality.
So please, before you get yourself into trouble at work: walk faster!