For a lot of people it is much more basic; family either doesn't want to take-over the business, or just isn't up to it.
The founder sells to monetize their life's work, and continues to run the business for both health (mental/motivation/physical) reasons, and something to do. Done well, it's a second wind that works well for everyone, and which can take many well into their 90's.
Often great businesses to work for, as they have both industry brains, a deep bench, and the capital to do meaningful and successful innovation. Also a lot safer, as they've been through the business building process, survived it, and fully understand the inherent business risks in their industry. The buyer just needs to make capital available as needed, and stay out of their way. All about emotional intelligence.
SD