I get the sense some people on /r/sysadmin are almost like mercenaries who go anywhere that will pay them the most and they don't care what they do or where they do it.

Normally it's only the employer who is not really loyal to employees, but in some cases the workers are also expressing their ability to not pledge fealty to an employer. That's basically what I'm getting from your comment, that you should feel grateful that you're being underpaid so you can get a case of beer per week.

In the past five years, the benefits for staying at an employer for me included:

1. A five year 401(k) vesting schedule. Five years. So each year the employer match only came in 20% increments, meaning that 6% match or whatever it was really amounted to a 1.2% match per year.
2. A five year sabbatical. I have to wait for five years of being underpaid to get a trip and PTO for a month. Woo woo.
3. At another job, I had to wait six months just to get enrolled in the 401(k).
4. At another job, the 401(k) started right away, but then the company pulled the 401(k) because they were acquired by another company.

Other than whatever the defined contribution plan is at a company, there's really no reward to staying at a company for an extended period of time. Many people are in a position where their jobs can be eliminated tomorrow by an H-1B after years of good service to a company. There's no pension plan anymore for most people.

So why stay, especially when moving jobs is really the only way to get a pay raise that beats normal inflation rates? I literally doubled my pay in the past year by moving into consulting, where staying with my last job was causing health issues from stress and applying for other similar sysadmin jobs is a painful process in and of itself.