This question almost always gets a particular kind of answer here -- framed in terms of some kind of personal limitation or shortcoming. The person has no identity or sense of self-worth outside of their job, or they are workaholics...
There is truth to that -- plenty of people do struggle in retirement because their jobs define them, etc. -- but there's another side of the story, one that you don't typically hear on this forum (it's part of what I meant when I talked about the skewed sample).
Few people here seem to appreciate (or at least articulate) that many people choose not to retire for
good reasons -- not just because they lack imagination, can't think of anything to do but watch TV, are workaholics, etc.
So, in the interests of providing a little balance, here are some "good" reasons why someone might not want to retire completely, even if they are FI:
- They enjoy their work
- They find a sense of meaning and contribution in their work
- Their work is a source of learning and growth
- They like their colleagues and the social stimulation of work
- They benefit from the intellectual stimulation provided by their work
- They enjoy exercising a sense of competence, feeling effective at something they've trained all their life to do, and do well
- Their jobs give them a feeling of being useful and productive
- They like the extra money, which is beyond FI so can be considered "free money," to just blow on whatever they like, without concern for financial security
- They don't want concerns about rising health insurance costs
- They like the variety that comes with alternating work and non-work days, so that "days off" retain their sense of specialness (vs. every day is a day off)
- Their work is low stress and provides plenty of freedom
p.s. I should add, what I'm thinking of here is part-time work, what some would call semi-retirement. I'm not thinking of full-time work, in perpetuity. Let's not get carried away.