When you look back on the lives of people who work for more than 15 years in a single company, especially if its a corporation, we are able to tell a different type of story most of the time.

Childhood. School.
Teenage School.
Post Adolescence. College
Adulthood. Company.

Yeah a single company, and the colleagues turn  into families (sometimes) or game of thrones. Its like a support system for the entire life. Get in the company, and your life is set. That's the notion they have, or they fell into. Well its not a bad thing to have a very stable life, except for the fact that such a life is not tested enough to bring the individuals full potential outside. But ofcourse the job designs in some roles are really great for a challenging learning experience.

The new trend, especially since the Gen Z have started to enter the market, we will see shorter and shorter time span of commitment to one single purpose (from a project perspective). Many are already job-jumping and it is being justified by the business journals too. The trend now seen is 3 years to 10 years [un-cited].