Bill is 54 years old and was a slave for most of his life. He would never have run away if he hadn't accidentally killed his master's daughter. Hannibal found him within hours of the incident. If not for Hannibal Hamlin, Bill would have been recaptured within the day or fallen prey to the Wasteland's dangers. Bill isn't that skilled and has no military training. He's been relegated to cooking and cleaning, and he's an awful cook. His other principal job is to take care of the Brahmin and Four Score the dog. Bill has spent his whole life afraid and subservient. Even though he is free now, those habits are hard to break.
"Oh, ma'am, this place is heaven. Just a little bit of heaven here in the wasteland. Any slave makes it here, he's free. Just like that. And, Mister Hannibal, he's got a plan. A plan for heaven to be everywhere, not just here."