This is an interesting question, indeed. Changing work environment? I think it will depend on your motivation and personal goals. There are lots of people that feel comfortable in their current jobs because it allows them to have a nice lifestyle, afford their expenses besides the sense of stability they can feel working there and that is enough for them, So they could spend their entire lifes working for one only employer.
But there are people that don't like to do always the same due to they hate routine or just because personal and professional development have a greater influence over them rather than labour stability good wages or any other benefit. There are people that feel motivated while they are learning new things or see opportunities for growth.
Personally, i can not do the same routine for my whole life. I changed my major when I applied for my master and now I am working in Africa as a mandarin teacher. But I already thought about changing my job again. After 3 years teaching chinese, I think it's enough. In case of one day i would hate my job, i decide to loking for something more interesting.
It's not that much critical how often they change their works. What's important is that they acquire something skill which can be acquired only by working on site. I think so.