Many of my senior colleagues have worked for the same organisation all their lives. Usually these people are "don't fix what's not broken" types. They have their job, their house, their families, their hobbies, their routine. They like it. No need to rock the boat for the sake of rocking the boat.
It also says something about the quality of the employer. These people are esteemed experts and have plenty of places that would gladly have them, and probably pay them better too. If you have options and choose to stay, it's a good review for the company.
The record goes to my previous workplace, a public authority, there was a woman who worked there for 50 years, and said she had no intention of retiring anytime soon. She had a photo on her desk from 1960-something, it was her as a newly employed teenage secretary in the company of senior colleagues who today are all long dead. Pretty surreal.
