I noticed recently that one of my coworkers has been in his job for 30 years. My father and father-in-law both retired from teaching after 30 to 35 years in the classroom - each was even in the same school for their entire career.
I can't even fathom it.
I've not been around long enough to have worked for 30 years anywhere but in the last 20 years I have worked for 7 different agencies/companies - not counting contract work or position changes with those employers. I don't feel like I've switched around a lot; each move has been logical, due to change in location, education or family circumstances. And I don't know that I would have wanted to do any of those jobs for 30 years, except maybe the work I have done at my son's school.
I like the new challenges that have come with my career variety. I like the new skills I've learned and the new relationships I've built.
For me, variety beats longevity.