That's just one way of looking at it. An acquaintance of mine who is also a HR guy once told me its in a person's best interest to keep hopping companies every ~3 years at least.

Working at one company for a long time can be interpreted in many different ways. More like a person, who isn't excited about looking for new opportunities. Or a person who is just lazy to not make a move etc etc. Also if you stay at a company for a very long time, unless the company gives you a generous raise every year your salary will be way behind market standards. And if you are OK with your work being valued so little for so long, it only means two things either you just agree that your work or contributions aren't very important to be paid enough, or you are just lazy. And both are negative indicators.

Its pointless to show loyalty that spans across 1.5 decades to a mega corporation where the boss two layers above probably doesn't even know your name, let alone the work you do. No wonder they don't blink twice before letting go some one. As much talented you might be, and how many algorithms you've memorized or how many nano seconds faster you can make a program run.

I fail to understand why anybody would stay so long, its like setting yourself up for a big meltdown sooner or later.