Or be too embarrassed to admit they cannot afford to retire..........
+1 to this.
I imagine there are tons of 60-70+ women (and men, though not the subject of the OP's linked article) that just aren't subjectively financially well off enough to live the life to which they have grown accustomed, so they stick with a job to provide an income to fund their lifestyle (while possibly collecting SS, pension, annuity income, withdrawing from retirement funds, etc).
There are fun social and intellectual aspects to jobs that many find appealing, but I would argue those are positive factors outweighing the downside of jobs (stress, time consuming, inconvenient) that fit into the equation of continue working or retire fully.
My own mother is one who would fit into this article's headline. She retired 2 years ago at 62 but couldn't stay retired for long. After volunteering at a few places they quickly offered her paid employment ("hey, if you're doing this for free you might enjoy it more if you get paid and we can formalize the arrangement that way and come to rely on you more").
A part of it is social - my father is still working and I'm not 100% certain she wants to spend more time with him than she does know. She likes to get out and see other people, and it seems like me and my kids are her main social network (help!!!!!
), so part time work fills that void for her.
But she's also subjectively worried about finances (in spite of a million or possibly several million in investments, a nice state pension and a couple years away from unreduced SS x2, with expenses probably no more than $60,000-80,000/yr). These jobs basically provide pocket money so she doesn't have to touch her investments while still being able to spend on travel like she wants to. Objectively they could probably spend well over $100,000 per year with a 100% chance of portfolio survival, but I can only do so much to persuade them to spend my inheritance. As a result, she works in retirement.