Some people may value the people that they work with and the loyalty they get and give, more highly than they value the money. I don't think this is stupid or underacheiving in any way. Working with people you feel close to can be a great experience. As with investing it's a matter of risk vs. reward. If she is content with the way her life is, and the way her life is going, it doesn't make sense for her to risk that on the potential that she may, somewhere down the road, be as content somewhere else.
If you've found a way to be happy, why not stick with it rather than being perpetually dissastisfied because there may be something better.
It's refreshing to see some intelligent discussion, I was beginning to get worried. Without a doubt there are some serious psychological "things" at work, for both Tripp and Bill's wife. Being content must surely be near or at the top of the reasons one would not at least look into something else. What I read in your post, maybe a bit between the lines, is that there are not degrees of contentment per se. That being the case, it would be impossible to be more content so she would have no reason to even look. . .or maybe there are higher levels of contentment in the workplace, but those levels can never be realized without taking a chance, so people just stay put.
I don't know why so many people land in a job and stay put. What's funny is that before you're hired you don't know that'll be the job that pushes you to contentment - most don't go into the interview dreaming of working at the Hertz Reservation center, it's only after they are trained, get to know people, and get comfortable do they "stay put for good".
I know there are a great number of people out there who are unemployed, but need a job. They find a job so their need for a job is satisfied so there is no need to look any further.